As far as I can see, the Improvement plants do nothing. Come to think on it, if you add in the setting of Only Colonise breathable worlds, that pretty much makes the Planet Utilisation Tech a waste of space
Oh yeah, the AI is hopeless with this type of game. It sits there with its mineral facilities going full crank, and then doesn't scrap them when they start producing 0 minerals. I was playing a no warp points game and was getting a whole bunch of systems hooked up, had my resources budgeted out real good.... had a look at the AI empires and said, damn if only I could charge them to use the warp points I created
Even one of the neutral powers (that don't leave their home system) did better, they got a whole two warp points opened.
If I see a Finite Resources game on PBW, I'll go for it, like. It pushes you to really expand, and combined with settings like Only Colonise Home Planet Type and Breathable Atmosphere, it makes the remote mining a lot more useful, especially if you're having to pay maintenance on a warp-point opener and want to spread it around a bit.