That's a hard thing to call, Bruce. If you make an old song too "authentic," it's hard to convey the message of the song to your audience. If it's an unrehearsed group that's singing the song together, it can be even harder. Folk songs lose their connection to the "folk" of the present time if they are treated as museum pieces.
On the other hand, if you modernize a song too much, it loses its connection to history. It's a delicate balance.
When I lead a group in singing a song in dialect, (e.g., Scottish) I guess I usually try to downplay the dialect as much as I can - partly because I don't do dialects very well. Some people resist that, and their attempts at sounding Scottish or African-American or whatever can be quite ludicrous.
I think that folk songs are living things that have the ability to allow us to communicate with the souls of past generations. If we are too strict in preserving the authenticity of a song, I'm afraid it can become a dead artifact. As long as the songs live and grow and change, and as long as new songs are continually added to the canon of folk music, there will be no demise of folk music.
-Joe Offer-