Though I absolutely hate radio commercials in real life, I love them in SH4
Personally I prefer to have short files: say 5 minutes maximum for talkshows/comedy shows. As much as I enjoy listening to Fred Allen or Jack Benny, hearing the same shows gets annoying. I suggest using "edited highlights" for shows that have a lot of talking. Sports games would also be a nice addition, of course here also only the highlights.
As for music, how about using not just the song but also the voice of a presenter introducing it.