I would think that the 70-200 is definitely going to be too long, except for possibly picking out details and isolating them with DOF. Although even then, you may have to be far enough back from the car that people will keep standing in front of you. Generally, wide is good for the reasons mentioned above.
I tend to work with a 2-body set up, to avoid constantly changing lenses. I use a 20D with 10-22mm for the real wide angle work, and a 5D with 24-105L IS for general work. Both are fitted with flashguns, but only for a touch of fill-in, I use ambient light for the main exposure. I don't carry a monopod or tripod, or a camera bag as these are a real encumbrance when working in a crowded environment.
IS is generally better than a fast lens as your subject is normally stationary, but be aware that cars on turntables may show some motion blur if you have to shoot with very slow shutter speeds. In these instances, bump the ISO up or use flash as your main light.
The 28-135 will do a decent job, apart from not being wide enough in some cases. You will probably keep getting frustrated, standing back to get a shot and having a stream of spotty youths standing in front of you to take a shot on their mobile phones.
Personally I like to use a flash at around -2EV, although that value will vary according to conditions for each shot. This allows it to lift the shadows and put a sparkle into headlights etc., without actually affecting the main ambient exposure. Using flash as the main light source is prone to results with heavy fall off as you are frequently within a few feet of the car, so the back end may be 3-4x as far away as the front. That will result in very underexposed rears.
Get there for when the doors open, try and be at the front of the queue for buying tickets (or ideally buy online so that you can just walk in). Once inside, head for the supercars / concept cars that are likely to be popular FIRST. You have maybe an hour or so before the crowds start getting thick, use this to good advantage. Later on, the exciting stuff will have a thick crowd around it at all times, making it difficult to get close and change position etc. As crowds build up, move onto the more bread and butter stuff.
If there is a live action show, book a middle of the day performance. It won't make any difference to that show, as the seating will probably be full for all shows, but it means that you are not missing out on the main static show as that area will be teeming with public and no fun for photography. If you can specify seats, don't pick ones too near the front. That may mean that you will be shooting through the top of a safety fence, when the cars are coming closer to you. Live action shows may be tricky for you though, as IS won't help much. I switch to an 85mm f1.8 lens for these and even then need 1600 or 3200 ISO quite often.
It is well worth hanging around until the end of the day, from mid afternoon onwards the crowds will start lessening again. The last hour, maybe two, will be quiet enough that you can find room around the star exhibits again.
Obviously, good camera bracing techniques / resting on solid objects etc., will pay dividends in the relatively low lighting.
The above is my personal way of working, others may not use flash, or may use tripods etc. Each to his own, according to what they want. This works for me and gives me the results that I want.
