I've breadboarded the circuit a couple years ago with a copper clad blank as the antenna. It did work, I was able to control the LED brightness but I never actually paired it to a circuit.
It's not a stupid question: You could just use an expression pedal or build the effect into a wah shell and have a pot instead of the LDR. The probe circuit is a way to do remote foot control for a parameter without the associated mechanical design issues of having a moving treadle turn a pot shaft.
Personally, I think it was a bit of a gimmick and since I can't think of any other pedal manufacturer who has nicked this idea, it doesn't seem to have been a popular success.