here's my suggestions that might make the game more fun to play since as you guys said that this will be a living game.
More cars - last time got those cadillac and escalades, it will be fun to customize them also. Nissan 350/370z, audis, hyundai veloster and genesis, evo10, latest civics, impreza stis, ford focus, eclipse, rx8, peugeot
More customization - more decals , monster decals, more headlights and tail lights option, roofscoops, more front and rear bumper options, more bodykits
Drag event - not sure if this can be done as there's no manual option but it will be fun to test cars with friends on a straight line racing with or without traffic