I panned the Wen many years ago. About that time there was a chap living in a van parked by the river who was (barely) making a living panning for gold (Welsh gold attracts a premium, just because it is Welsh). I have not been back for years (too far) and I read somewhere that floods have swept the rivers clean (don't know if this is true, or just a ruse to keep the competition at bay).
This site is interesting and worth a visit:
www.scottishgoldprospectors.co.uk/
and I was gobsmacked by this recent thread on mindat:
http://www.mindat.org/mesg-17-100868.html At least panning in a river will not upset those who object to collecting down mines. You'll just get the anglers moaning at you instead!