Hi Bruce,
No, you didn't scare me off it. I watched it as planned. While not knowing that much about the Carter Family aside from their music, I can still see your points. I enjoyed the first half hour with all the photos and archival footage. Nice to see Gillian Welch briefly demonstrate and break down Maybelle's sound (if not the technique) as well, something that seems uncharacteristic in this sort of PBS doc. But yes, the second half hour was far too preoccupied with the breakdown of AP and Sara's marriage, and left the music behind. And yes, still not enough Maybelle, but that footage was great.
Overall I thought the thing was far too short and superficial, not using the little time available effectively. Pacing was odd. Their recording career was compressed so much it was over almost as soon as it started. The music wasn't explored much, despite some promise early on with the discussion of Single Girl, Married Girl, AP's song-hunting with Leslie Riddle (would have loved more information here!), Maybelle's guitar style etc.
Some enjoyable bits sprinkled throughout but overall I agree with your tepid response.
cheers,
Andrew