After about 20 hours, gotten to the point where I have nothing left to do and raiders pose little to no challenge. I find that I have so much gold and nothing to do with it.
I like the idea of paying money to annex cities in different biomes with different environments. Maybe the towns have issues that need to be addressed or are overrun with raiders. Would give a nice challenge after completing the basic game and give you a reason to continue building without starting over.