I've found that aside from their humorous aspects (e.g. the Snathi), the minor civs really add nothing to the games I play. Basically, they're a source of easy money/tech via trading (their diplomacy generally sucks) and, once you get Planetary Invasion, an easy way to get a high grade planet with a bunch of nice improvements (like tech/mfg captials).
I'd love to have an option to turn them off, or even better, be able to set how many minors will appear. The game would definitely be more challenging without them, as the AIs can't exploit them to anywhere the same degree as a decent player.
Thoughts?
Cheers
h