I'd like to see 3 things fixed or added:
1) Naval invasions
2) The ability for players to influence AI diplomatic relations
3) A strategic AI where the computer has a massive monetary edge so they can just out spawn you. This would disguise a lot of the other strategic flaws the AI shows and would actually allow for a sense of accomplishment when you are successful.

Those 3 fixes would make this a much better game IMO.