Something that might be fun for a game that is about an ongoing war would be if the player gained rank and/or achievement titles during a campaign for achievements (and/or titles gained) in the game. It could be based on how many planets you took, kill score, knowledge (science) gained, how much you unlock, etc.
A ranking system that looks like:
1) Fighter pilot
2) Pilot commander
3) Starship pilot
4) Starship commander
5) Fleet commander
6) Fleet Adm.
Achievement titles:
1) Murdoch Gov.
2) Resistance leader
These rankings and titles could be completely different depending on what you unlock or the campaigns. It would be simple and positive feedback to the player on their gameplay.