5 is actually 100% perfect in explaining how headphones are in my life, i don't spend insane money on it because there are far better things to spend it on in my life.
My music is far more important than my headphones, give me a choice of headphones vs music and ill listen to speakers for the rest of my life . I guess you could call headphones a means to an end for me.
I voted 9 because it is pretty much true although I would question the use of the word "investment". Although 7 certainly applies to me as well. Actually my wife is pretty much the only reason that I haven't spent more. Which is probably a good thing!