This will sound crazy, but when I was a kid my brothers and I played City Trial until we unlocked all of the vehicles for Free Run, then made up a meta-game where we all started out with a Wagon Star, a small amount of "money", and a house somewhere on the map. Everybody then had to perform some sort of task as their occupation (destroying trees and coral, patrolling rails, trying to break somebody else's car), which would earn them more "money" to spend on a better house or vehicle. I have no clue how or why we came up with it, but it was fun!