It feels like your trying to find a vision here, which is a good thing.
Simply trying to make photographs like the car pictures in the car magazines is pretty much a lost cause -- it's insanely hard to light cars in that "car advertisement" style, and you typically need a bunch of gear. You can do it with light painting and less gear, but it's still a hell of a technical chore.
The idea of sticking the car in the graffiti covered area was solid, I think. I hate the light you've got here. It's eerie but weird-looking. Again, it feels like you're trying some stuff out, which is awesome, but I think this particular aspect of the experiment doesn't work well.
I would have put the car into the cement stall at an angle, and then climbed all over.
A snooted handheld flash can be pretty effective. Just roll up a newspaper and tape it to the flash, and then use it like a squirt gun to spray light on the car right where you want it. At night, with a long exposure, you can even do some light painting using multiple pops, manually triggered. Anyways, I happen to dig the look a snooted flash gives on cars.