Here is an exploit I found interesting. Play as Altarians, research Precursor history and Divergent evolution. You'll get Biosphere Modulator, a one per planet project that increases planet quality. Build it, decomission it, build it, decomission, repeat this and planet quality will skyrocket. Well, no one forces players to to this, and AI won't do this but it still is tempting, and unbalances the game. I got PQ up to ninety-something, even tough there are "only" 72 tiles on planets. Maybe the PQ should drop after the BM is decomissioned or at least not grow after it is built again on the same planet (using a variable for every planet to remember, if that improvement was build on that particular planet so that PQ only grows once from it would somewhat solve the problem, but msking PQ drop to what it would be without BM if it is destroyed would be better).