Thats sick! I think it should mainly be a bard spell because of the music, and I love how you added that you can make your friends auto succeed :)

it is. and it is a modified spell version of what the The Pipes Of Haunting does. The Pipes of haunting is in the 2014 players handbook. the reason why the version of the spell says that it applies to the dragon song guitar is because it is a spell that was to be added to a homebrew instrument for one of amember of my party but that instrument idea was scrapped. but the spell works for any instrument. and that instrument that might've been added to the bards weapon list was called The Dragon Song Guitar. maybe you might find some use of the spell when using a instrument.

also, you could turn any weapon trait into a spell but with some modifications. the only thing i would say about turning weapon traits into spells, is that if that weapon trait does more than 1 die roll of damage then you might want to test it first an make that spell a level higher than a cantrip. but obviously frightening a bunch of targets doesn't really do damage. and if that weapon trait you are turning into a spell does 1 die of damage, make sure to add the correct damage increases at certain character levels, like how the Fire Bolt spell and other cantrips add extra die rolls at certain character levels.