Trading with the AIs in the latest version

More diplo definitely helps.  

'Good deals' are rather relative.  I rarely get a deal that's even vaguely fair until I've got a giant diplomatic advantage; what makes it work is that you can turn around with the tech you just payed a swingeing price for and flog it to the rest of the galaxy.  Human players are typically much more aggressive traders than the AI, and you can get back several times your investment by aggressively reselling 'techs.  

Trading IP for anything is grey.  IP aren't terribly valuable strategically, and a lot of players think that it's an exploit to use them to suck the life out of the enemy economies.  Though there's a certain deep plausibility to the idea; 'influence' used to get sweetheart contracts, obtain secrets from corruptible individuals, have newly made warships sent via third-party dummies to one's own fleet; the fact that the AI doesn't use it, and one is basically trading trash for treasure, means the practice is considered an exploit by the purists.  I use it relentlessly.  

The AI are rarely willing to give you a 1 on 1 deal (you have to outdiplo them massively), but unlike the AI you actually understand what is worth what and what isn't. I usually don't retrade techs I've gained in trade, but I do trade the techs I have to everyone that is willing to give me something of worth, greatly enhancing the tradeprofit per tech. That way, I still get a "fair" deal.

As for the IP thingy... Well, you are your own moral compass. IPs are close to worthless, and as the AI will not trade anything for IPs over 999, you can't even trade IPs in quantities that may shift the elections. If that is to stop you from trading them is entirely up to you.

Is it just me, or do the AI's consider planets worthless? They seem to be worth so little to the AI's in trades. I'd have thought these were the most important things in the game.

The best trade deal I have gotten recently involved a mining starbase I owned.

I had added enough modules to get it to +34, but had never put defenses on it -- I regard those as almost pointless at Suicidal as the AI sends big fleets.  I was at war with two AIs and one slipped a fleet past my pickets just as I committed the local defense fleet to support the invasion of one of the AI's planets.  

When the AI fleet got to the starbase, I traded it in a nice deal to another AI.  Of course, I was careful to chose another AI that the enemy AI was also at war with ....

Then, when the AI fleet moved on, I re-constructed the mining base.  Maybe I can do it again?

The AI values planets based primarily on their population. Getting them to give you a high-pop world is almost impossible, but they don't care very much about planets with only a few million people (though there are exceptions, as I've been unable to trade for certain particularly valuable newly-colonized planets).

with IP you can basically vamp AI's econ. 100 billion credits at a time. hehehe

You really need massive diplomacy. With it you can sell 999 IPs for low level techs ... and 1000+ IPs.