Uke,
My experience doesn't extend beyond Western culture so I can't comment on the examples you cite.
I agree that the informant should have the final decision as to what use the material is put to; so as long as he or she is kept informed the collectors can, as far as I'm concerned, use their own judgement. Some discretion is needed on the part of the collector; not so long ago we had the case of a vindictive reviewer who chose to openly insult elderly traditional singers, but this is extremely rare.
Can't really get my head around the idea of a 'paying public'; sales of CDs and books of traditional material are so small (certainly in the UK and Ireland) that it is simply not an issue, or certainly hasn't been for a long time. Gone are the days of Chas McDevitt and Nancy Whiskey squabbling over the royalties of 'Freight Train', which of course came from Elizabeth Cotton.
I sometimes find myself irritated by the story of Bob Dylan 'stealing' Scarborough Fair from Martin Carthy and giving it to Paul Simon who copyrighted it and used in 'the Graduate'. That particular version of the song was collected by Ewan MacColl and Joan Littlewood from a retired lead miner named Mark Anderson, and used for a radio programme called The Song Collector. Too often the role of the source singers are overlooked when discussing source material.
I find it bitterly ironic that the extremely rare ballad 'The Maid and The Palmer' (only 1 recorded version - 'Well Below The Valley') was copyrighted by successful Irish musician and broadcaster, Phil Coulter. The informant, Traveller John Reilly died of malnutition in a derelict house in Roscommon. The collector, Tom Munnelly, donated the proceeds of the recording to a school for Travelleler children, who, I'm sure never saw any of Coulter's royalties.
I can't help noticing the difference between the US, where there appear to be a number of collectors and researchers working full time, and this side of the pond where, to my knowledge there is only one professional (employed by The Irish Folklore Department).
I once reviewed Sandy Ives' excellent 'The Tape Recorded Interview', which I found tremendously helpful until I came to the chapter on signing contracts for the use of the material. Our relationships with the people we have recorded really precluded our getting a singer or storyteller to sign a 'release form' at the end of a session. For me, it would suggest that there might be some benefit from the songs and stories other than the personal pleasure we got from listening to them and from the knowledge that they had been preserved for future generations to listen to.
Best wishes
Jim Carroll (who has gone on far too long - as usual)