I don't think having silver on the drones makes burger all difference as there are enough great sounding sets of pipes from various makers out there without any silver on them. I suppose it's feasible that only pipes made out of the best wood would have silver put on them (although not in the case of McCallums apparently).
I've never had a chanter with a silver sole (Robo does!
). However, I have heard people say they reckon a silver sole adds a bit of brightness?
...Need to add another question to the poll, asking whether people who think silver makes no difference, actually have any silver on their pipes or not. Possibility for bias here!