When you unlock a new race, how about a message box appearing, introducing the newly unlocked race? With a suitable congratulatory message of course :).
This is a great point… and a good opportunity to give the races some interest to them. Maybe some suitably gratuitous backstory. =):
Great suggestion. The presence of multiple races isn’t even evident at first. It should be more visible so that players know it exists and how to work towards them. They should also be trumpeted with fanfare when they manage to unlock one.
Unlocks can be a great addition, but they require a few things to be useful:
 They have to be interesting enough that players want to work towards them. Different races certainly fits this category (although they might be disappointed when they realize it’s mostly just different graphics).[/]
 It has to be clear what exists to be unlocked (even if all the details aren’t there, they need to know that they can unlock it).[/]
 There needs to be a clear path to unlocking content. People who are drawn in by unlocks generally aren’t puzzle solvers, they are connect-the-dots people. [/]
 There should be some way to track your progress towards unlocking. It provides feedback that what you are doing is working and it gives an indication of progress which drives these same people towards completing the unlocking process. [/]
 User’s should be informed and celebrated whenever they make further progress, and especially when they complete an unlock. This is a major part of the drive that makes them want to unlock things. [/]
For more great examples, just look at the achievement system that Blizzard built for World of Warcraft.
Hmmm. So what would make a gratuitous backstory? As a writer, this strikes me as a fun thought experiment.
Let’s see. I would imagine it would be fun if the races were exaggerated cutout examples of sci-fi stereo types.
The federation might be super goodie two shoes types, trying to save the galaxy from itself but myopic, they might easily pick the wrong side to help.
The Imperium as hyper vicious expansive and internally super strict… but their people love it… (or will say so if you ask them… while their overseer is there).
The Alliance plays the part of the bug eyed aliens… extra big and clickety and obviously disgusted by the human meat bags…
Finally, the rebels… a righteous group stereotypically fighting for freedom… though not sure what they will do once they have it. Fun stuff.