Well, Steve, mate,you know I'm pig-ignorant on these matters but I think I'd call an instrument non-acoustic if it can't be heard unless plugged in (like a solid body or a keyboard). Where you draw the line beween playing an acoustic instrument into a mike or with a pick up I don't know. Once they start using effects pedals I think you can safely call them non-acoustic!
I agree with you on volume, in general PAs seem to be set at the threshold of pain
RtS