Quality Vs Quantity

Well I think its more an offense/defense issue. If you can harm his ships, but he cant harm yours, then you win, as easy as dad. As long as you can do damage it pays off to pour a lot into defense. The goal is getting the ships that last longer. 

Quality. I play DL only, and it's rather dull to see my destroyer types maul one Iconian or Torian fleet after another without hardly losing a ship (both create scads of 'peashooters'). I play as the Yor (for the mini bonus amongst other things) and I can pack a LOT of firepower on a small hull.

Early in the game, you don't need much defense as weapon atk values are small. As the game progresses and atk values begin to climb, it pays to increase defense. But at some point, atk values will swamp even the best defenses you can put up, so I go for cheap, all-attack smalls and use wolf-pack tactics to take down big-hitters. I also employ what I call "gunships"...a cargo hull crammed with engines and weapons and little else. I use these to take on an enemy's toughest fleet. My fleet will go down but they will make a very serious dent in enemy numbers. I then move in with a 'conventional' fleet to finish off whatever is left. 

I havent made it to end game tech, pretty much ever.  Something always happens and I dont finish a game.  I have probably played about 200+ hours of Galactic Civ II and I have never finished a game. Usually when I reach a point I know I am going to win or get stomped, I get bored quick and start thinking about what I am going to try next, and before I know it, I am starting over.

I was curious how end game battles played out, with everyone loaded up with tech, but it never seemed like it would be fun.  I do like the cargo hull idea, I made a few ships once with cargo hull and a few Hit Point addition modules but I cant remember why I gave up on it, maybe to expensive? I'll have to look into it.

Starting from cargo hulls and adding hit point addition modules will probably end up being more expensive than a regular hull. Cargo hulls are great for suicide tactics such as Klaatoo describes.

It depends on difficulty and which races are being used: sometimes the AI will go after weapon techs so aggressively that you can't keep pace with your defenses and still have decent enough offense. In those cases it's more advantageous to go with full offense.
In huge galaxies I tend to prefer quantity over quality so that I don't have any undefended planets and don't have to keep an eye out across long borders for any spore ships and the likes.

Another consideration is that if you have Twilight expansion installed is to go with fleet booster modules (fleet warp bubbles and the like). 

The thing is that ships are programmed to ALWAYS attack the ships with such parts FIRST.

Create a stone wall ship with such a module and create a nice fleet of offense focused ships with one of them.

Of course, if the SW ship fails, then prepare for an expensive loss.

As an example of how absurd it can get, in a recent DL game, there were freighters running around with an attack value of 127...and this with Disruptors which have an attack value 1/3 that of the Doom Ray. 

So at that point there's no reason to mess around with defense at all unless you build nothing but BB's and Dreadnoughts, which I don't do. Any starship with a maintenance of over 30bc just isn't worth it, for me, and unless those 'heavies' are battle-hardened vets with a huge stack of HP's, even they won't survive, at least in my experience.

That's why I build nothing larger than 'mediums' with enough defense in mid-game to take one hit. Once the high level weapon techs start showing up, I dispense with defense altogether and put on weapons only and outproduce whomever I'm fighting.  

So the basic jist I'm getting is Defense can work early game, but end game its almost usless. I'm going to actually try and finish my current game this time or at least get to end tech to check it out.

One reason for my obsession with defense is its realative cost in research to weapons techs in TA. Its much much quicker to research defense. And I usually always align with Good, and get the defensive techs that go with it.

FYI I have been playing on "crippling" difficulty. Before that "Painful" but I was winning most of those games fairly easy.

It's worth pointing out that the uselessness of defense in the endgame is primarily found in DL. I don't know for certain whether it still winds up ineffective for a maximizing player, but for someone who doesn't worry about that kind of thing, defense is much improved with the DA/TA combat system. I'd say it's still highly useful in the endgame, especially in TA with its hit to military research.

I hope you don't enjoy watching the combat viewer, though - high-defense, low-weapons ships in combat makes for long battles.

Yes, sorry if I wasn't clear enough. I play DL's only, so changes made in DA/TA I wouldn't know about.

To get a little further into the DL system: the Doom Ray (highest level beam weapon) has an atk value of 22, costs 150, and requires space of 10 +4%. The best shield defense, Ultimate Invulnerability, has a defense value of 9, costs 140 and requires space of 3 +3%. So you need three UI's to counter the Doom Ray. The space required is about the same for both systems, but the UI defense in total will cost nearly three times that of the DR. 

The story is about the same for Mass Drivers and Missiles. It will cost 2 1/2 times more to counter the Blackhole Eruptor missile, and close to three times as much to counter the Black Hole Generator mass driver. 

The time factor required to build a more expensive starship led me to just dispense with defense altogether, at that point, go all attack, and attempt to outproduce my adversary. If I can produce three mediums or four smalls while my opponent is building one BB/Dreadnought or two mediums, I will win.

 @ jakecaptiva

I get rather bored with endgame play, but for a different reason. Usually, when you get to the last three of four civs, a big "Mexican Standoff" results. Everyone is allied to everyone else, and noone wants to make the first move and have to fight all the others at once. If I make the first move even though one of those civs was my ally from way back in mid-game, they will fight for the other side. It then just becomes a huge attrition slugfest. Every DL game I've played ends up this way, so I just start another game.