Hi Richard,
The engine bay in my TC is just plain fibreglass with black paint and AFAIK that's normal. My car is a one-owner and the guy was meticulous in writing down everything he did to the car (even petrol & oil ! ) but there's no mention of doing anything like removing silver foil.
I would guess it was someone's attempt to suppress radio interference; cover large areas in foil and then earth it ?
Brian