I'm a keen proportions player, and I would say that although Mylon's suggestions in the previous post are well thought out, I would vote against all of them except the increased range of cities. Sorry Mylon
I like the economics as they are now. The new range of cities would be an utter nightmare to implement and upgrade, but would be cool. Maybe you should try to get a more flexible upgrade system into the next patch before attempting to implement them.
One thing I will suggest though is a set of combination bonus facilities - ie fleet+ship training, citizen databank+computer complex etc. Have it so you can upgrade to them from the singular Versions.