I haven't time to reply to you in the obsessive detail that you deserve--but I will make a couple of points--first, and sadly, the tamburica (sorry if I don't spell it Walter Kollar style) is not the much played by the younger musicians(at least among the Serb and Croatian nationals) the play accordian,and write and play songs, just like musicians tend to do--because they need material to play for the dancing--my little kolo was an U Seste that we stuck into a medley for the oldest reason of all, because we didn't know more than one tune for U Seste, and the dancers called for more--

As to the Hoppa Hoali music--most of it was written by Hawaiians, but even that that wasn't was played in the ethnic style--slack key guitar is very popular, but the ukulele and the steel guitar are just as traditional, if not more--

I think it is important to distinguish between folk music and material that happens to be traditional in the sense that you discuss, because the music of a particular subgroup, like worksongs, may exist as a body only as long as the subgroup exists--even if it is only a generation, the body may still be valid folkmusic--some elements may be passed along to other situations and other generations, and some might have been drawn from previous generations and such--that would be more in keeping with the idea of traditional music, as you are presenting it--