Galactic Civilizations II: The Dark Avatar

Take “extreme colonization.” In the original game, you could be boxed out of the space race if there were no friendly environs in your immediate area for you to settle. Now you can research technologies that let you colonize planets generally hostile to life - water worlds, radioactive worlds, high gravity worlds, etc. These research paths become so important in the mid-game that your neighbors will pay a high price to acquire these secrets, maybe too high. At this point, trading terraforming techs is a great way to buy all your rivals’ research.