Hmmmm, this is a topic I deal with often. Whether to use the coin-op or not. Really, for most younger people, a coin-op is the only option. The other day, I was washing my wheels with a wheel brush, and accidently put my hand under the high pressure water stream. :shocked That really, really hurt.
Then, I looked at my car and wondered, "I bet if it could talk, it would be screaming like I did with that high pressure stream." LOL
Guess I will make an effort to clean more at home now, I do worry about the dirt that usually remains after washing the car at a coinop. Really, no matter how much you spray the car, dirt will remain on it. The towel you use picks up the remaining dirt, which can cause scratches, of course.
But here is the problem, what if you are in a place where you can't wash at home, what then. Coinops where I live don't allow bucket washing, and usually you have that person behind you hurrying you up to get out of there. Now, I would rather my wax get scratched, than my clearcoat, that is for sure. I have several coats of wax on my car now, and hopefully that helps.
Don't see a solution to this problem, except maybe using a QD during the dryoff at a coinop, but most QDs want a dry surface, and by then it is too late for this role. Not to mention you don't want QD all over your drying towel.