Along with being able to make our own instruments, how about a guild skill where we could make an instrument weapon ala Bard's Tale? The bard in your party was able to use a fire horn which would blast out fire scorching enemies. I realize that it might be too powerful scorching a whole room full of critters. How about a battle horn of sorts that might cast some tonis bolts, a mass lullabye, vibration chant, etc...
Or even just a battle horn that can alert nearby characters of a need for assistance? Just a thought I had.