I usually use my 17-70mm f/2.8 Sigma, however I also use a speedlight with a diffuser. You need some depth of field to get decent shots of the entire car. I normally go down to f/4 or so for detail shots and f/8 or higher when I need the depth of field.
As with everything else though it will vary from one show to another. The most common spot where they are held here has horrible lighting.
Indoor car shows can be tricky. I've been to a couple with really crappy lighting and some with decent lighting. IMO, the only thing you can really do is bump up your iso and use noise software later if you need to. Luckily the d90 has a good sensor for that. I use the Nikon 17-55 f/2.8, and Sigma 70-200 f/2.8 hsm.
It is difficult, and given the circumstances you've got some good shots in there. The show lights both hurt in some places and help in others but all in all you did a good job with what you had to work with. One thing to keep in mind at shows like that is that the vendors spent a lot of money designing the lighting and displays to bring out the best in their vehicles. Rather than fighting it the best thing to do is find ways to work with it.
I seldom go to new car shows but hit several custom shows each year. Certainly none of them are as large as anything in Detroit but they are still fun and challenging.