I have to say that the Galaxy is probably my least favorite Enterprise, including the ones rarely seen (B&C). However there are some ships from other races that I think are worse. There was a Rom science ship, or scout (don't remember which) that I really HATED, but then again I didn't care for the TNG handling of the Romulans (those forhead ridges make me irate!) I love the big warbird though.
As for an expansion to SFC3, there would need to be a lot more done to it than just adding older (tmp/tos) style ships to it. Not that I feel it needs to be SFB style, but it certainly need mounds more content and depth than the initial offering had. That's the opinion of every gamer who's played the game, that I talk to anyway. Would it be too much for an "expansion" or would it just have to be a whole new game?