I heard a good programme on Radio 3 (BBC) yesterday which was talking about how Bartok worked out, only toward the end of his career, that it was easier to improvise on Hungarian / Romanian folk music than to write his own, which is what his peers had done for some time.
The music were dances of various sorts, some of which were not performed until he had died - some subsequently conducted by Mahler.
Just thought you might be interested - nice set up too!
David