There's crap in the music of every era and every genre. Just because a song is interesting and important from a social study or academic viewpoint it doesn't make it de facto a great song, it needs more than that. And many great songs of the past may be unpalatable to contemporary music tastes or their subject or language may be offensive to today's mores - this doesn't make them bad songs, simply out of time.

I see the 50's/60s revival partly as an accelerator to the normal folk process, which went on before then and still goes on.