Always the same tune while playing the music instruments

Well, if you never use the "perform" interaction, you will get no or very low tips. This will go up in the tens of thousands simoleons per tip if you perform exhaustively. You should at least try and get to about 25 performances (can be done quickly by canceling after the first notes appear) to get any reasonable tips.

Anyway, I don't know of any solution for "play alone".