If you guys are right, we could mount a pickup on something like styrofoam, or a sponge, and tone would be identical to plastic/wood. Be interesting to see I guess.. Wood sure LOOKS cooler... Since the pup is not stationary but actually vibrates with the rest of the guitar, I can't imagine the material it's mounted on / wound on wouldn't make a difference, as it changes the relationship between the vibrating magnetic field from the pups and the vibrating metal strings. Is it an audible difference? Dunno. Probably less noticeable than changing to a different type of pick.