I think to get a nice effect, you need to have the car highlighted in some spot lights. This can be tricky to do. It's possible to do with multiple slaved flashes, but positioning them can be tricky. Plus the light quality of most outside lights will often screw up the color balance of the photo.
A lot of work to do, but it could be rewarding. I think Madn3ss did some pretty good night shots a while back.....
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