With regard to the danger of the automated car wash...
It was only a year ago that I sold my silver 1988 BMW 735i 5-spd, which during those years was rarely waxed, was periodically washed, and was always garaged. A pull-through automatic car wash was almost always used and then the car towel-dried under close observation. When sold, the car looked like new.
Because of the extra care I wanted to give to the black paint job on my NSX, I opted to use a service that touted the superiority of hand-washing the car. I didn't doubt the advantage of the hand wash, until I watched those guys sloppily move their sponges and towels around the wheel wells and along the lower edges of the car where these instruments were bound to pick up grit, and then casually return to washing or drying the more visible paint surfaces on the hood, rear deck, and upper doors. I even watched as one clown more than once dropped a rag to the ground, picked it up again, and resumed scrubbing the paint surface. GASP! I think they were surprised when I asked to drive the car away still dripping wet.
The above illustrates the potential chasm between theory and practice. A good hand wash is more thorough and safer than a automated wash; but a careless hand wash can be worse. As long as I don't have the time to give my car a hand wash that I can trust, the local pull-through car wash will have its appeal.
The wheels on the M5 are an altogether different issue that may disqualify the pull-through car wash. Does your $20 hand wash service have a franchise in Atlanta?
Richard