One of the things I believe is lacking from all version of the game has been the insight to what other factions are doing. You can find out who they like etc but but you have no idea to the extent of their empire, number of cities the balance of their forces the boundaries of their empire etc etc.

I feel the game would benefit from a mid game unit/building that could provide intelligence on other factions. The closer you are to the faction the cheap it would be and the more info you could get. At the basic level you would get 

1. number of cities/citiziens income etc

2. extent of their boundaries, i.e., you could see their empire on the map.

3. battles waged - get a quick over view of who they were fighting and the results of the battles.

I think an intelligence building would be the best option. You could assign gold per faction, more required for hostile. Maybe have it so that when at war agents stop sending info.