Interesting topic. In the case of "Wildwood Flower," I assume Maybelle was going from her memory of what she'd heard, as we all do in various instances. Better to sing and enjoy than to get hung up on academic perfection. Now we have access to the original, and more sensible, lyrics. I prefer them because they seem less like nonsense, but if you're singing with a group who knows the Carter version, you either go along with the gang or make it a learning experience for them. Either way, it should be made enjoyable rather than pedantic.
BUT, then you have cases like Roy Clark doing "Yesterday When I Was Young" and singing nonsensically about his house "built to last on weak and shifting sand" rather than the original and understandable "built, alas, on weak and shifting sand." What, Roy Clark can't afford to buy the sheet music and get the words right? If he chose to make the change for artistic reasons, which I seriously doubt, that's his right. But I'd bet anything it was just a matter of mishearing and not bothering to check any resources. Since the song conveys a powerful message through its lyrics, I think he did it an injustice through laziness and unnecessarily weakened it. If I were singing such a song, I'd want to put a little effort into presenting it at its best.