So what is the design goal of reducing pop growth so severely?

I’m growing and expanding in my game but I don’t feel like the galaxy was colonized yesterday while I was asleep. I think they really took the nerfs to tourism to heart I wasn’t positive with cash until turn ninety although I am playing carbon based life instead of synthetic. I think they wanted to suppress the method of mindless colonization of everything and reduce the absolute necessity of employing Col Rush

Definitely done to nerf the "I Must Colonize Every Single None-0 Planet I Find" approach. Now you've got less people, you've got to ask yourself if colonizing that particular planet is really worth it. And adding the artifacts, that approach is even more important now.

For me, I always avoided the Less-Than-10 planets until I'd colonized the better planets. I was playing Tall for my own enjoyment, I think the game was - and Frogboy even acknowledged it once or twice, I believe - totally designed for Wide (ie Colony Rush) so that was the only way to win. Not played Retribution far enough yet to so how things work out now, but I'm really liking it so far.

Well if the goal was to slow down the initial colony rush I don't think it worked. Everything I have seen that is colonizable has been taken before turn 50. If I didn't take the ones near me, someone else already had colony ships on the way (including Mars in the Sol system).

So the planets are all taken, but with minimal pop on each. Research or production doesn't seem to have suffered as a result (as I said, I'm getting techs almost too quickly and I can building any ship in my tech base within about 2-3 turns). 

And honestly a massive hit to pop growth doesn't seem to help Tall at all. It will take forever for a planet to grow to a decent pop level and since you get at least minimal output from the colony bases it still behooves you to grab as much as you can, as quickly as you can.

A few other things of note:

'Wealthy' is extremely beneficial now. +1 production on every colony when most colonies are making 1-3 raw is a HUGE increase. 

Asteroid Bases are far more important than anything else now. My homeworld makes 8.57 production, FIVE of which comes from the nearby asteroids. That means that asteroids are basically make or break...if you have them, you're on easy street. If you don't you're likely to fall way behind. And what's the best way to get Asteroids? Yep, you got it, take every planet you can that has them nearby. 

So yeah, I still don't see the benefit/rationale for reducing population growth buy such a severe fact. Maybe .05 instead? 

As it stands now, population has gone from a major contributing factor to the economy to one of the weakest. I'd much rather than 5 colonies each with 1 pop and an Asteroid or two than 2 planets with 3 pop each and an asteroid or two. The former will produce 15-20 raw and the latter 8-10 raw. It's just no contest and it seems even more tilted in favor or wide now.

If you want to slow colony rush, remove the huge wad of cash that everyone starts with and make colony ships cost significantly more. That's the way MOO2 did it and it worked. You simply weren't able to produce large number of colony ships until you had tech'ed up and developed a bit. They were a massive drain on econ. Of course in MOO, you had to make the choice between production or science which is not necessary anymore in GC3 but even still if a colony ship took 15-20 (or more) turns to build you'd be a little more selective about where to send them. 

Alternatively, you could make population growth a fraction of available pop on the planet. So then keeping a decent pop base on the world might pay off more short-term profit than flinging them out in penny-packets to every available world where it would take a long time to realize any benefit. 

But as it stands in Retribution, the changes seemed to have ENCOURAGED colony spam and Wide, not discouraged it at all.

One poblem of tall vs wide is population limits based of planets vs. civilization. If it was civilization based instead of planet based, everyone would have the same population untill you start hitting the population caps on the planets. if it was civilization based instead of planet based let's say still 0.1 per turn then added randomly to your lowest population with the highest approval planets then everyone would be getting the same production from population, regardless of having a few, or a lot of planets.

The same problem still exists when you have population caps on planets on planets. You would still need to remove that to make this work.

Correct, it's not pop growth based on a fractional amount of pop, but pop growth based on the number of planets you're on. So you get more pop the more planets you're on (however minor at this point).

End result though is that pop is a far less important priority than having nearby asteroids or other things that give magical +1 RAW.

Negating the effects of resources, and asteroids make no sense, unless you added this. There is a limited amount of bussiness based on the galaxies need based on the total population of the galaxy, and the entertainment, and tourism. This would limit the effectiveness of factories. Farms would also be included in this. This would then shift the balance of power. Then just having the most of everything wouldn't necessarily work. the one with the long west income would have the best factories is the most realistic.

The civilization with the lowest economy, and most influence. This would be alarmed betweenbinfluence, andaeconomy. to be able to sell the manufactured goods, and resources to the people first  this would be minused from everything based on total galaxy population that you met. This number could be different for everyone based on who is met. Banks would work differently than markets. Markets is what people can buy. Banks both finance business, and increase what people can buy. Banks, and stockarkets affect the number of businesses based on population like. Excess of this results in a financial loss. Depending on factors. As the total galaxy population increases this would also increase.

At the beginning of crusades they tried making less important by square rooting raw production instead nobody liked that, so they changed that back.

I think what it comes down to is that there's really no way to completely discourage colony rush, at best you can force players to be more strategic about it.

The fact that each planet has a growth cap (as they should) means that NOT grabbing every planet you can ASAP is a VERY BAD IDEA and always will be.

Ya, and now we're pretty much back to the same thing, but without the square root...instead, pop is just an insignificant proportion of your RAW now.

And it's still a colony spam, you just are hard limited by available pop (since it take a min amount to build a colony ship).

There are definitely better ways to prevent/discourage colony spam than the this pop reduction. I'm just not seeing any benefit from reducing it by so much.

Which is quite possible, but players don't like to be 'penalized'. And I think game devs now run in fear of Steam reviews from players who quickly spam out 'Not Recommended' reviews because they were challenged in the game. :/

Which is one reason I support Epic Games Store (even though they're no less scummy than Valve). 

But yeah, you can't really have a 4X game without the EXPAND part, that's one of the Xs.  What would be better, and it's probably too late for GC3 at this point, is DIVERSIFYING the expand options.  Generic Colony Ships being the only way does make that phase of the game a bit dry, Stardock is right to wanna liven it up.  Maybe things like allowing, say, Hippie Colony Ships that increase the Planet Quality of what they colonize, at the expense of a Production Penalty (perfect for building slow to blossom economy or research worlds), Barbarian Colony Ships that have a Production bonus, but their planets instantly culture flip should enemy territory EVER envelop them (disloyalty), Diplomat Colony Ships that give Influence and Moral bonuses, but suffer Research and Economic penalties (perfect for worlds that are likely to border enemy territory), and so on.

Again, too late for GC3, but can work if GC4 becomes a thing.

Edit - You can even enhance all this by allowing successful invaders/culture flippers to decide if they wish to keep the Hippie/Barbarian/Diplomat/etc. culture, or purge them for a generic one.  This would give Generic ones the advantage of not boosting your opponent, should they successfully invade/culture flip.

Add colonize class zero planets. I like the idea of diversifying colony ships.

That, or let us do SOMETHING with them besides blowing them up with Terror Stars and mining them as Asteroids.  Like maybe we can use a special ship to build a Science Station that studies the planet, netting us some research.

As an update, a handful of techs further down the line  and pop growth is up to a fairly good clip. All of my Cap:4 worlds are full and my worlds with Cities are starting to fill.

I would still think about reducing the raw production from Asteroid mines as they are still the single greatest contributor to your econ for a good while (including research which seems kind of odd).  And they are still randomly generated leading to situations where the strength of your early econ and research are dependent on randomly finding asteroids near colonizable planets. Of course it does give a nice incentive for war...

Whatever happened to radioactive, toxic, barren, etc. worlds? They showed up all the time in GalCiv2 and I thought that was a very elegant way to prohibit the early colony rush. It was like having a carrot dangled in front of you making you want to research aquatic worlds or whatever so you could be the first to claim it. I barely ever see them in GalCiv3. They should give an option to increase the likelihood of finding planets you don't have the research to colonize yet. That would solve the problem rather nicely.

They are already in game. 

How do you transform a dead world in a mining site?

You can create a colony module that terraforms a dead world into a class X world, but I don't know that you can make it spawn durantium or such...