This is a departure for me, because this is more of a turn-based strategy than an RPG, but it does use some role-playing elements. I thought you guys would appreciate this.
I was inspired by games like Sid Meier's Civilization and the new Sins of a Solar Empire. So I created: Solar Dynasty.
Once through questions...
You mention the bonus/penalty for population but never explain what roll (?) you make to get people to move, reproduce or how many a military unit kills per round.
Is 1 population (as in building units) one billion?
Why does two units on a planet require war? It seems that takes away the strategy of building up a military. Plus they may not even meet if neither one tries to colonize.
Does moving into orbit then to a planet take 2 moves? Does it take 3 moves to go from one planet to another (1 into orbit, 1 into a different planet's orbit, 1 onto the surface)?
Do you need scouts (with stealth mode) to use stealth on a planet? If not what is stealth mode?
The upgrading seems like it could be a problem if a player had more than a few planets, since keeping up the multiple count downs could be hard. Is there a suggested method such as dice?
Can multiple units be banded together? Ie. two military make a military that gets 4 dice rather than 2.
Does a scout have to find a planet? Why couldn't any other unit do the same?
I'll give another read through when I get a chance. The main issue I see is that not all events have mechanics and resolutions. A fairly minor issue really since you've got the bulk of the system.