[Shadowstar]

It might be cool to have the agressive empires differ in outrightly declaring war and alternatively making tribute demands and subjugation-style treaty proposals. This would give them more variety. You'd have some who just want to wipe you out of existence, while others who would rather dominate you through sheer power. On this vein, you could have genocidal empires who seek to destroy a specific race, irregardless of any specific empire. Every planet that contains that race would be a target, regardless of who owns it, unless its one of thier planets (in which case it would be something akin to a concentration camp). Another empire might want a specific race as a member and would pursue conquest or treaty options to that end. Not sure how much of that is possible in the AI files, but it would be a very interesting way to give the empires personality.