Hi!
Iztok - I'm jealous.
Don't be. I'm just imitating your gaming style, using more suitable Super Diplomat for that. And you probably know what's said about imitating.

but for me buying planets is tricky, and not something I can depend on yet. Are there any pointers you can pass on that I might be overlooking?
Nothing I'm aware of: I have ALL techs that increase diplomatic abilities (but last majesty, federation and last two ethic ones), and 've lease-bought Diplo Translators. The Galactic Showcase is pending (not in queue), and I still don't have the last trade tech for the "wonder" that increases my trade offers' values by 50%.
In fact I'm not doing so well. Too low research output (~50% of the best AI) to get more mil/soc production from focus. IMO I turned to 100% research too early. I'd probably fared better (built more labs) by keeping 1%/66%/33% for a dozen more turns, and buying one factory before labs. The only planet that's fuly covered with Basic labs and one Research center is Earth (a factory on a 300% production tile helped a lot there). The second one has 4 labs finished, and the rest of planets has one bought, two-three in queues, the rest are Trade centers. I don't generate lots of money from the trade-abuse: other AIs (9 mayors, 5 minors) simply don't have enough money to pay my trades each 4th turn. On average I collect only ~4000BC each 4th turn, and that's just enough to buy one structure on each planet and maybe two small-hull constructors, and keep running a ~300BC deficit. So at times I'm "simply" trading tech for tech, or for their research treaties (IIRC about 12 of them

), or for planets. Takes a LOT of time though

Techs also became more expensive, so I can't research so many of them to profit significantly by trading them.
BTW I don't get a ++ in relations from their research treaties. Like in your case I still have only the starting 40% econ ability, despite having Democracy and Trade centers. IMO two bugs.
Will report what happens further.
BR, Iztok