JP,
Being a Telecaster man myself ('58 original ) I feel I may contribute, certainly on the maple/rosewood area. Maple is varnished (or lacquered on earlier models). John's right about the tone, but it's the feel of the fingerboard that is important as well. There's more friction (and hence tactile feedback) with rosewood but maple's quicker. It's possible to play about 15 notes per second on a six string (and not strumming, I mean picking), so speed can be important. In age, the lacquer/varnish becomes worn and the fingerboard becomes blackened with gunge. This adds thousands of pounds to the value - funny old World. I've used maple and rosewood and they are very different to play.
My Ricky 4001 has a varnished fingerboard but that's not really for speed, but to preserve the neck, I'd guess. My Persuader is ebony so is smooth and quick, so it's unlike the relatively grainy rosewood.
As for the pickguard, it's plastic and not capable of holding much in the way of charge, and is of course a good insulator, so not sure what's going on. You might want to check your earthing, perhaps a ground loop?
Cheers!
Jas