For valet parking in general I've heard that if you would like extra special care taken when they park your car, tip at drop off and pickup.
The last time I valet parked was a year ago somewhere outside of chicago. When I came to get my car, they couldn't find the keys, then asked me if I was driving a pontiac, no a dodge. After about 15 minutes, they finally located the van. The guy who drove it up ( also the one who couldn't find it at first ) opened the doors for me, my wife, and my daughter then lingered like he was expecting a tip, well we just waited literally fifteen minutes in the cold, wind, and rain sheltered only by our umbrella because they were having quite a few problems that day finding the right vehicles. The last thing I was going to do was tip for service like that.
I don't own any exotic vehicles, but when valet parking comes to mind, I think of "Ferris Beuhler's Day Off" and what happened there.