I think that when it comes to cars, going overboard on HDR, has it's time and place. And it's so easy to want to push the photo to it's limits.
Personally, I despise any HDR that looks overtly HDR. If I submitted a cartoonish HDR image to any of my clients, they'd call me back asking "WTF is that $hit?" and that would be the last time they ever hired me for an assignment. I couldn't blame them, either. If I were in their shoes, I'd do the exact same thing.