I’m sorry if this have already been say but here are some ideas of improvement you could make (if possible of course)
About world creation : Why not make the world infinite with a large variety of biome (each of them having particular ressources and civilization on it !), to do so and not use all computer memory/processor, maybe you could use a chunk system kinda like Minecraft ?
If you make a world infinite in minecraft like, you could probably add more civilizations (Maya kind, Middage European kind, American Native kind, Asian kind, Arabic kind, African Kind, etc …) with real cities, ressources (exchangeable by commerce) and a siege system (real fortifications, siege engines etc.) !
Add water gestion (wells, fontain, irrigation, pipes etc.), water would be needed to survive (By the way, I sometime see my minions eating in water … Shouldn’t they drawn ?) !
Add reproduction, crazyness and lucre (Children etc.) making the game harder (you need to feed every one, and maintain peace !)
Add more job (Kinda like in Dwarf fortress and reality : cop, manager, bookkeeper, instructor/teacher, water distributor/pipes worker, warehouse manager, artist (dancer/singer etc !) and a lot more !).
Of course, these are just idea and that would be very very ambitious ! And you probably had all of them already !
Anyway, I already like the game as he already is now !