For some reason this reminded me of how in the game Lords of the Realm II, a highly populated province would have its main "settlement" look bigger and more advanced the greater the population much like in RTW. Your fields for growing wheat/raising cattle however, would be clearly represented on the map and could even be pillaged by your foes, causing economic damage as well as famine, possibly even starvation. Depending on how large your population is you'd eventually see small hamlets and villages popping up within the provinces borders, which of course could also be pillaged and caused direct population loss.

What would be really sweet would be if instead of just making the "fishing villages/mines/etc" simply eye candy that may or may not give you certain economic bonuses, you made it so that they were vulnerable to pillaging or at least razing via devastation. Granted this is most likely something that simply can't be done or at the very least could be done, but there is simply no way to make the "AI" use it. Either way it's a great idea IMO, albeit an unimplementable one given the "AI's" limitations.