I too had the car show lens question last weekend, so before heading to the Portland (Oregon) Roadster Show I did some web searching and found this:
12 Tips For Car Show Photographers | Photofocus
The Portland show is indoors so I knew the lighting would be lower than I'd like. I shot RAW with auto WB and almost no flash. I have LR4 so I can make changes later if I shoot RAW. The 18-55 kit lens is not usually my first choice on outings, but I needed the wide angle and from past experience I knew the show would be close quarters so why take a lens much past 75mm. I also took my fixed 35mm for kicks (but never used it, but should have given it a chance). Before leaving the house I lightened the camera bag by taking some stuff out which left room for my wife to put some of her things in the camera bag so she didn't have to take her purse, so she gladly carried the camera bag. I threw my Rocket Air blaster and lens pen in my jacket pocket so all I had to do was walk around and find great shots and take in the cars without dipping into the camera bag every other shot.
I put a polarizer on the 18-55 as per the attached article and it did a great job of cutting the reflection (also used a lens hood). I took a risk and left the monopod at home and just had to wing it on a steady hand. I lost a few shots because they weren't sharp, but I got plenty of good stuff. The so-so lighting, kit lens and going hand-held made for a tricky balancing act for good depth of field. It was tough to get the longer shutter speeds but I think things came out fine
One trick I stumbled onto was if you want better pics with less people to work around and a less cluttered background go late to the show. The Portland show opened at 10 AM and that's usually when we go, but decided to go later in the day and got there at 4:30 and had till 9:00 PM. I didn't think it would be enough time but people tend to head out for dinner and by 6:00 the crowd was so thin I never had to worry about other folks getting in the way and we got through the show quicker. It was awesome.
When you're doing a tight artsy shot be mindful of what's reflected in the paint. I got home and noticed a couple shots had people (who had been walking behind me) reflected in the paint and it took away from picture.
Don't get so caught up in the camera you forget to enjoy the cars.
Posted a few shots from the show. I did a quick scan of the 300+ pictures processed in LR4 and the focal length for most of the shots was between 18-25mm. A few were over 35mm and if they were it seems they were all the way at 55mm. Take note in the Vette/Cobra pic how there aren't a lot of people in the background because of going later in the day.