I haven't, but I've got 3 1/2" clearance to the tow hook and maybe 5" to the front valance. I'd drop it another 1 1/2" but there are 3 bump strips between the street and my carport.
The best one I've seen I can't find using site search, maybe someone else will recognize the description. It was a Metro/Civic-like vehicle with a conveyor-belt airdam down to 2-3", like you say, in front of the tires but was notched up maybe 2" in the center.
I think this would do two things. The extra clearance delays high-centering on gravel drives, etc.; and the center section didn't have the curvature of the ends to resist deforming so it's gets relieved for less pressure.
For some idea of the pressure involved look at this air dam:
Look how thick the aluminum plate is, and the number of fasteners to hold it on the car. These Beetles don't run much above freeway speeds.
You might want to use something like spring steel fingers or something on the upper backside.