On thin metal, sand (or more likely glass bead blasting) can leave panel distorted rather than dented panels. I had a non-mini shell bead blasted by a reputable company. This shell had very thin metal and no problems occured. If in doubt, consider chemical dipping - places like redistrip. There's a few in Melbourne, a couple in Sydney. Check your local area. The only problem for the home restorer with either method is that it will remove all traces of paint everywhere. A lot of manufacturers dip-paint bodyshells when new up to half way up the a pillars, then top coat the lot. It's hard to get paint back into some of the recesses with a spray gun.

KB

just buy a twisted wire attatchment for your angle grinder works a treat on anything (including bog and surface rust) took me about 45 mins to do one side of a clubman.

If you do this though, it can leave gouges or swirl marks in the metal which you need to use hi-fill primer to cover, same with Orbital sanders (unless they are random pattern - usually air driven specialist panel beater tools rather than your electric 1/3 sheet sander).

If you're doing a full on bare metal resto, you don't want that.
KB