As a UK person who has never heard the Prairie Home Companion radio show (and can't afford the bandwidth/log on time either) and so isn't qualified to judge Mr Keillor's singing voice, can I say in his favour:

his stories are wonderfully written and the recordings he has done of them are superb (he at least has a superb speaking voice); and

the songbook he produced (Prairie Home Companion Songbook?) was a great idea and carried out really well. The idea that one definition of a 'folk song' was a song you never learnt but seemed to know any way, and asking his listeners to submit their 'folk songs' made a very valid contribution to the sort of thing we've been doing with Mudcat. So we've got children's songs, scout and guide songs, parodies and lots more. I bought the book in the UK (sadly it was remaindered.