I would not agree that the song is necessarily more important than the performer. I think it's all about communication, and sometimes the performer can more effectively communicate his vision by taking liberties with the song as it was given to him.

Jazz is a good point of reference for this. To take a well-known example, when Coltrane performed My Favorite Things -- a lightweight ditty from a lightweight musical -- which was more important: the song or the performer? How about when Monk performed April In Paris?Or when Robert Johnson performed some of his cobbled-together blues, using assorted verses from other, older songs, was it the song that mattered most, or the expressiveness of the performer?

In my opinion, there is no need to construct barriers to creativity. If a particular performer chooses to express his vision by radically revamping a traditional tune, why would I discourage him?