I mean, I think you're right in terms of placing re-singing within the folk tradition, and I know that voicing can make a huge difference. You mention Buffy St. Marie; I was already thinking of Joan Baez. I think part of what caught me off guard about Jeff Buckley is that I came to him along a singer/songwriter path; it's like the reverse of folkies getting mad when Dylan started writing his own stuff and went electric. In general, I don't think I've figured out what happens to aural/oral music traditions once recordings exist.

I'm also kind of chagrinned about how much stuff Britten wrote that I didn't necessarily know he wrote until way after I loved it. What a composer. Relatedly, would love to hear you sing Lyke-Wake Dirge sometime. That sounds perfect.

Nina Simone is a whole other thing, because she said on many occasions that it made her angry when people imitated her interpretations of songs; she thought of it as plagiarism. I'm not sure whether I agree with her about that, but it's something I think of whenever I hear someone doing Nina Simone, including me singing along.