In some places - not just city - the venue valets all cars to a lot off-site. Many times it's quite a ways down the road.
Perhaps I'm in the minority, but I took a local trip in valet mode the other day and I thought it was just fine. The performance edge was sawed off, and it's now worse performance-wise than giving your Chevy Malibu to the valet. Perhaps he'll drive it to "look cool" but it's certainly not going to be a performance demon for him to show off.
The issue that I have now is the valet playing with the screens, settings, etc. I'm not worried about the 70 mph aspect, I'm actually more worried about a valet messing up my settings, or my entertainment stations, or whatever. Lock it down except to the front page of the "controls" screen, IMO.