The beauty of folk music of any country has to do with it's idiocyncratic elements that is reflective of the culture that it comes from. I think it's important to be aware of these musical elements and incorporate them in a reinterpretation of the song or music.

The songs that have been written by certain writers have been successful in being able to do this. Woody Guthrie was influenced by The Carter Family who was in turn influenced by the reservoir of country music in the 20's in the US.

Blues songs have their tradition.

The problem with the contemporary songwriter is that so often these songs are influenced by 60's rock and roll or pop music more than they are the folk traditions of the country. This is a problem only if they are thought to be folk music. There are other songs being written today which have a great sensitivity to the traditions of folk music and their folk "style" can be very convincing as reflecting the specific cultures. For example, Tom Paxton's "Ramblin' Boy" or "Last Thing on My Mind" to my ears sound very much akin to the folk country traditions of music. "Spanish Is A Loving Tongue" is another which has a cowboy feel although it was composed by Badger Clark, a poet and rewritten by a cowboy singer.

The point it this: it's important to be aware of the musical traditions of each song that the musician attempt to reinterpret who is not part of that tradition. No reason why any of the music or songs can't be sung by anyone with this in mind.

Frank