An alternate tech victory option for AI factions. Instead of ending the game when an AI researches tech victory, that race simply disappears from the map and all of their planets become available for colonization. To prevent abuse, make all of the tech victory techs above Discovery Spheres non-transferable like the spore tech.
I like that; it reminds me of the ascended Ancients from Stargate. I think their planets should keep their buildings as well. Then again, it may depend on alignment: good races may want to remove their buildings so that it wouldn't change the balance of power in the galaxy, while neutral races might not care that much about it. Evil races... well, evil ascended beings would do horrible things (I can think of two examples on Stargate SG-1 in later seasons); maybe the present behavior should be retained for evil races that get a Technology Victory.
Another issue: 'Starport Full' and minor races. In the game I'm playing now, the LentzLandians clogged their starport with freighters; I think they took up all ten slots. If they can't have that many trade routes, they shouldn't build all those freighters. Maybe the AI should be coded to never build more freighters than they can use (possibly they should start building them again as they research the next trade technology); I can't think of a good reason to have ten freighters if you can only have six trade routes.
Also, on a related note, minor races seem to fill their starport a lot and then stop building ships. Maybe they should scrap older junk heaps to make room for new ships (or, if they're the same size, upgrade them).