[SoYank]

Judging by picus's location I'd say GTA stands for Greater Toronto Area.

I agree that the original looked cartoonish but it did keep you attention. The black on black doesn't work for me because I can't see the car that well. The silver on black works just a little bit better. If you're concerned with the cartoonish car, why not just replace it with the silver car? Alternatively, lighten up the background from black to a dark gray.

Have you thought of using silver for the lettering? Especially if your car image is silver.

I'd suggest leaving the back plain; maybe put a small map to your shop (if you have one) at one end and leave the rest for notes, etc.

One last thought. You say you don't want to change your website. There is a possibility that people will get your card, go to your website and think they're at the wrong place because of the difference. I'd consider taking the same design of the card onto the website.