Cosian has brought up a good point. Don't be like Aaron and ship the game with only a half thought out mod as your "stock" game. A quick and dirty way to get a semi well-balanced mod might be to mimic one (or even *gasp* a FEW) of the strong mods out there right now in the SE universe. HOPEFULLY, it would just be a matter of a few quick conversions to SL's unit measurements, and a few beta tests to yield a decent "stock".
As for the leaders, that is kind of a neat idea. Don't just have Combat leaders. Have a mine boss that increases a planets resource production by a couple of %, or an Albert Einstein that boosts research on a planet by a couple of %. a few points, though.
- A. Leaders should have a limited lifespan.
B. Leaders that practice will gain % bonus, while leaders that don't will lose %. (Stick Albert Einstein on a research planet, and his bonus will slowly increase. stick him on a mining world, and it will slowly decrease.
C. Leaders should spawn on planets without regard for their proficiencies. (Einstein was the son of a salesman, after all).
D. I have no idea why A is the only item to get a bullet in this list. 
I'm not personally a fan of the "rare resource" paradigm.