It would be cool to have some more vehicles about, and a larger variety/quality grade of vehicle components.
Some ideas for vehicles that could be spawned:
Mobility scooters (small electric engine/storage battery/box), could spawn in malls and houses.
Busses (large, 6-8 wheels, lots of chairs, big engines).
Sports cars (light components, superior engine/muffler, no storage).
Police cars (regular car with a siren component that creates lots of noise, perhaps storage containing firearms).