Every auto photographer i've seen/read/talked to said to get a good one. They reduce glare AND light reflections on the cars immensely when used properly. I've seen photos as well, where the author says that he used the filter to do just that.
yah almost impossible to get a great shot at an auto show simply becuase lighting is not controlled.. there are lotta people around and it just basically looks like.. well. your at an auto show haha.. but for what its worth the photos are well exposed and the angles you chose to shoot from are good. so now if you had a controlled environment i would suggest applying all of this to ... that =)
The only way i can see to take good shots at a show would be to shoot it like street photography, like trying to get shots of people getting their first look at their dream car keep an eye out for unusual carractors doing unusual thing around the cars, take a look at the old Life mags and see how they told a story