I think it would be awesome if thew landscape was dictated by your empires value system and how they treat it. Meaning if you value your enviroment ther land in your empires borders will turn lush and productive, basically a paradise that is unspoiled. However if your empire values industry over the enviroment or is an evil empire your lands will turn into a blasted wasteland, and the closer to your capital the more intense the effect(For both good an evil) There should also be an intermidiete mix.(Border regions between to opposing empires)
Here is an example. The fallen manage to conquer a large chunk of territory out an empire that values its enviroment. Over the course of time the enviroment changes from prestine forest to a volcanic wasteland.(Due to empire values, magic spells and empires preferance) This could be reversed if the territory is recalled by the empire that values its enviroment.
Also the lanscape should confer bonuses, for example the fallen prefer the dark twisted lands (Similar to Mordor, so therefore thy would recieve combat and resource bonuses if they have a city in that area) These bounes decrease or disappear in different land types, for example a recently conquered settlement in a sunny happy woodland area would confer no boneses or even impose penalties however trhe longer they are able to hold the settlement the land will slowly change to their preferred type and thus they would get there bonuses again. This could also be reversed, the humans take a chunk of fallen land and over time it turns from a dark wasteland to a pleasant area for them to live in.
Of course these changes need to take place over a long period of time as rapid changes is kinda silly. And since these games can go on for a long time it would be a cool feature.
I hope I managed to convey my idea clearly, I hope you also like it too. 
