Not sure if this has been mentioned before, but as an MMO player, to me, the only way that I as the player would feel connected to an in game character would be if there were a level of char creation and one that sticks with me through the main campaign. Honestly, as awesome as I think that would be, that's a lot of work for something not a lot of people would care about. As long as the cars themselves have a level of personal attachment (progression in power, cosmetics etc), I'm ok.
Another way to go would be to allow players to join crews/gangs or whatever you want to call them to promote unity in the game. I fully hope to meet other players here that I can go up against in game while using ventrilo or TS so I can talk trash to them while I slam them up the rear