OK, I'll cop to it: I do play bluegrass on occasion. But I do know
the difference, at least I think I do. My question is: are there any
recommended resources for learning the standard tunes? Is there some
Internet archive with MP3s to learn from?

I play guitar, mandolin, autohoarp, and (most ineptly) fiddle. I'm
mostly looking to improve the fiddle playing. The concept of
regional fiddle styles fascinates me but I don't know the first thing
about it, or how to go about finding out. But it sure seems like
something I oughta know before I croak.