If you keep playing , you'll end up with everything anyway. It happens like this for me....
"Oh that's a big multiplayer race, lots of racers in there....wait, I don't have that track...." CHA-CHING!!!
"Oh that's a big multiplayer race, lots of racers in there....wait, I don't have a car from that class..." CHA-CHING!!!
Then once you get a car from a certain class....
"Man, everyone driving car X in this class is smoking fast, my volvo must be slow...." CHA-CHING!!!