I'm guessing you might have read it already, but I think you'd like Flow by Mihaly Csikszentmihalyi (sp?)
Watching the
TED video from this author made me feel a little better. Not that I am new to the concept of flow, but partway through there is a graph showing flow only happens when adequately challenged. The neverending challenge of music might be what keeps me hooked. The challenge itself can be an excellent purpose of this creative outlet.
I'll go ahead and feel some resolution with the simplified logic of
happiness = flow = skill + challenge 
Sounds like this is may be an existential question projected at music.
Right on. I'm working on a fun personal project related to my profession, (not music) and even though it's "pro quality", I'm running into the same question of asking what's the point. So it's not fair to pin squarely it on music just because music isn't food and shelter. More of an existential question possibly beyond the scope of this forum.
In other words, music isn't some island of pleasure in a sea of wretchedness for me; it's just one of many things I like doing but which isn't as important as most off those other things. Thus why I 1) often don't see the point and 2) feel the need to make extra-meaningful music if that's how I'm going to spend my time.
Same here, I feel like it's common on musician's forums to see people hating on their crappy jobs or lives, but I like my 9 to 5 and the rest of my life. There are other important things I could enjoy doing, but music is an entirely different world based on emotions that can't be quantified or analyzed (not exactly anyway). The challenge of making something that goes beyond normal reality (getting heady here) has a certain allure to it.