Another mystery story that LaMarca might have mentioned, but didn't seem to (hope my hurried reading didn't just pass over it) is "Bimbos of the Death Sun," (author?) which skewers filk songing, SF "cons" and includes a folksinger character as well.

And, in light of the mention of cons, there's the newish SF novel "Fallen Angels" by Jerry Pournelle, which includes quite a bit of SF fandom with references to filksonging.

Stories of "the life" using performers in other idioms are also found. I recently read a good mystery involving country singers, and my wife has just finished reading yet another, which she's recommended to me, but I can't remember the title to either just now. Maybe later.