After reading the reviews and messing around with this game a bit, I like it, will be playing it for a while but can think of two improvements.
1. A storyline/campaign.
All the reviews thus far have pointed this out. It's a good game, each race has a backstory, but each war is pretty much a random skirmish.
2. A 4th race.
Whatever is chasing the Vasari empire is a good idea.
Combine these into an expansion where each race has a storyline and several campaigns, taking out sectors of the galaxy at a time instead of all of it at once, then once they've almost won, the 4th race shows up and starts beating the crap out of everyone.
You could even have pre-cursors to this; "pirates" that have never been seen before that mysteriously show up and are hard to kill in previous missions.
Think Dark Avatar for Galactic Civilizations.