Go early or don't go.
I know that sounds crazy, but it's true. The place completely clears out at 9am. If you want to park in the main lot, you need to be there well before 7am. If being in the main "show" lot is not important to you, then you can arrive later (7:30 or 8) and park in the second lot or even in the structure. Or you can wait in line until someone leaves the main lot; those who arrived earlier do sometimes leave at 8am, but then you've missed half the time you could have had seeing the cars and talking to people in the lot. If you are driving in from a distance, you will feel like you missed out.
Lots of very cool cars, but if you want to have time to enjoy all of them, you really need to be there early.