Changing a wall's length could'be the first step.
Which of the following mechanics you think that can be changed without any minor drawback to the game? Any strategy proposal that changes theses dynamics? It could'be either by a new upgrade or a strategy (Preferably by a strategy to add more variation to the game).
City:
1. % Income grown rate of a city (neutral or captured).
2. Total income earned of a city.
3. Max cap of income grown of a city (neutral or captured).
4. Whole country bonus.
5. % Population grown rate of a city.
6. Max cap of population grown of a city.
Misc:
7. % of encountering rare units.
8. (Air, Naval, Land) detection radius.
9. Amount of SP earned per battle.
10. ?
I'd add %chances of TBs but the amount of critics I'd get are so damm high.