Hi - sorry, didnt read all. No, dont think its a useless skill at all.
My dh is extremely musical. He took up the clarinet in secondary school as a hobby - he was from a "bad" area with many of the kids getting up to some sort of trouble and was encouraged to put his energies into the instrument as a positive distraction almost.
He can sing, he can play the clarinet, guitar, piano, tin whistle.. aw, loads.
Hes now a Military Musician, hes been in the army since he left school - its a fabulous job, secure, pensionable - they play in the concert hall, alot of PR gigs, Presidential visits etc..
He works on average 15 hours a week which enables him to spend a nice bit of time with our dd and help keep things going at home while I'm at work. He also earns 10k more than I do! (and I work 40 hour week!!)
Hes starting to gig now, in local pubs, functions etc.. its a way of socialising for him in a way, hes doing what he loves and still brings in a few pound.
People love him at parties etc.. because he always starts a sing song - takes out the guitar and it makes everyone feels happy and have fun!!.
Dont think its a useless skill at all! (its our livelyhood!)
His biggest complaint is that his parents didnt encourage him more with music when he was younger. He thinks he could have done even better.