Nice rolling shots, they are relatively easy to get right in daylight... at night is another story....
As for rigs, i have been doing a lot of research into this, and myself and another photographer and going halves in a setup. Most rigshots are done with the car off and just rolling it at walking pace with an extended shutter speed, as you mentioned, running a car while having a rig attatched can make the rig vibrate, but that comes down to a few variables, a brand new, stock as a rock car, should have little vibration when running, and especially if its an automatic, a
modified car with a cam/supercharger/turbo, trans
mods etc an vibrate and shake more violently and as a result, destroy what could be good photos.... By rolling the car at low speeds you also lessen the risk of if something were to fail on the rig and the camera were to fall, with the car rolling it only has to drop to the ground, not bounce along it at speed if it were being driven... This has happened at 190km/h+ and although the camera and lens survived and worked it was a little worse for wear...
You also need to remember that suction mounting can damage paint and panels of cars, i have seen examples of suction mounted rigs destroying the roof panel of Supra's and other things. Mounting on glass if possible is a better idea, and near as you can get to folds and bends in the panels. A lot of car owners will not let photographers attatch rigs to cars in fear of damage, knowing what repairing show winning paint, or even exotic car paint, can cost, i dont blame them!
I have played with small rig's, getting stuff like this
http://drmphotography.net/wp-content/ga ... g_2246.jpgImage too big to post, but just an example