the tour vehicles are pickup trucks with seats in the back and canvas canopies, open on all sides. the dust is incredible. if you take the tour, i would strongly recommend keeping your camera in some kind of protective cover, otherwise you'll get dust everywhere. it's so fine it will get into the focus ring of your lens, in the switches on the body... i have a camera rain cover that works wonderfully for keeping my camera and lens pretty much protected from that kind of thing... you can get one here.
i was there in June, and drove myself... got to spend more time at the spots i wanted, and stop where i wanted, and got some fabulous photos, so for me it was worth it, even though i didn't get back into the "restricted area". from the photos i've seen, IMHO the best scenery is in the main part of the valley, accessible to anyone.