"Rather than hoping casual listeners drop in on the off chance, wouldn't it be better to aim specific music as specific audiences with a bit of intelligent presentation?"

It may be that we are coming from two different countries with two different audiences, but the answer to your question is not easy on either side of the Atlantic.

I would hope that you DO want casual listeners to drop in and discover what the music is all about. Narrowcasting to specific audiences is risky, especially when the hardcore audience that you are talking about is such a tiny portion of the landscape.

I love to listen to Joe Heaney, and I love to show the music that blossomed out of the community that he so well represented. Contemporary folk music is made in the same fashion that the songs Joe sang were originally made, the mode of transmission has changed with the times. Audiences seem to have a positive response from the diversity that shows the roots and how the branches have spread.   

It would be nice if a program that focused entirely on source singers and singers of folk songs from the tradition could sustain itself with a large and supportive audience. Here in the U.S., shows of this type are offered on listener supported radio stations. Limited donations would mean a short shelf life for that type of program. It is unfortunate in many respects, but it is the way radio works here.