I think this goes both ways -- sometimes we broaden an existing tradition, sometimes we narrow it. An example of the latter is modern blues musicians who disdain to use instruments or play styles that the blues patriarchs were a lot more liberal about. Listen to old recordings of the Delta blues musicians from the 20s, 30s and 40s -- they incorporated a wide variety of instruments and styles into their work, presumably without worrying that they were compromising their own authenticity by doing so.

Eric Clapton provides an interesting illustration. On the one hand you have his well-known rendition of "Crossroads" with Cream, which he took in a direction that was decidedly different than the Robert Johnson original. At the other end of the spectrum you have his more recent CD "From the cradle...", in which he did note-for-note renditions of blues classics, right down to the little vocal asides that the original artists probably did that way once (on the day the song was recorded). Each of us gets to decide which of these exercises had more value; for my money, I think "Crossroads" did more to further the tradition by NOT sticking that close to the original.

I've never cared much for self-conscious authenticity; I say we should play what we're driven to play, and let others decide what they think about it. Then again, I don't get many museum gigs.