if it's any help now, heres a couple of tips from me 
take a zoom lens, a fast lens, and a midrange lens (i took the 50mm 1.8 and the kit lens, all i had, did pretty good.)
show your frustration to the crowd, so they stop getting in your way, then thank them kindly when they stop for you to take the shot
take more than the 1 or 2 shots of the same subject, on long days, and in less than perfect lighting conditions, chances are alot will have camera shake or simply be OOF because you've rushed it, take a couple, then review them carefully.
get there REALLY early, and try and get the top shots out of the way before the crowd comes, (ie; using a 50mm 1.8 prime gets a great photo, but you have to be a fair way back to get the whole car in frame)
talk to as many organisers and show-people as you can, you'll get different info from each, so you can try and know when the good stuff is happening. 
don't leave until all your CF cards are full 
talk to the owners of the cars, see if they have any special mod's or anything which are really really impressive but you haven't spotted yet, take photos of it
how'd you go, anyway?