well there are some automatic tunnell washes that I would sooner drive my car through than about 90% of the hand car washes I have seen.
The big problem is that the hand car wash places use their wash mitts and drying towels too long before they are cleaned. It's usually up to the guy working in the car wash when to decide to clean off the wash mitts/drying towels.
Which is nooooo good. Those guys don't give a **************** about your pretty Porsche.
I see these filthy SUV's go through righ in front of me and the workers will just do a quick dunk of the wash mitts. That means there are probably 20+ cars worth of debris in the sink before it reaches your Boxster.
And I've yet to visit a hand car wash (usually small ops) where they used a drying towel that wasn't CRAP with ripped binding and loose threads. As a matter of fact I wouldn't even let them dry the car. I'd give them a tip and ask them not to dry the car, pull over and take a waffle weave out from my duffle bag of detailing stuff.
I had a few black cars before, one of which was freshly painted before I bought it. After only a few months of hand car washing I could see spider webbing and swirls. And I once bent a $350 BBS RK wheel at one of those tunnell washes.
p.s.
^ A high pressure stream of water will not hurt the canvas, actually you should use this but avoid going near the weather stripping. I use an oxo feather tip car wash brush while rinsing to dislodge spotts.