I'm still not entirely clear on how this would have worked, but I think your original scheme was to carry both the guitar signal and the LED voltage in a single circuit, with the guitar presumably going into the input of an amplifier, correct?
While you could have made that work, another problem would have been a tremendous "Thump!" out of the amplifier every time you switched inputs. You could probably have filtered it out somehow, but as I said earlier, it would have been something worthy of Rube Goldberg. The double-pole switches are actually a much more elegant solution.