Well, this is pretty much the way we're headed already, right? Since the more civilized areas of the map have much more settlements, and every one of them can be developed much further, we need some trick for barbarians to stay competitive. Cutting their expenditures is the most logical way to do this.
And as for barbarians eyeing the riches of civilization... there is no need for them to even hold civilized settlements. With my traits, I can make it so that they recieve some hideous amounts of cash whenever they raze a well-populated city. We could basically create a role-playing experience for the barbarian player where he comes back every two decades or so to "milk" those decadent idiots...