First off, I have to say, your dilligence makes me feel lazy, and that's coming from someone who clawed his way into the profession from the level of "homeless bum living in his car."
Clearly, hard work is not your problem.
Also tight is your portfolio, and you seem to be doing all the right things when it comes to networking and volunteering. I think there's a lot of validity, however, to what @maryshaw said about focusing on your most productive networking and volunteer opportunities. I'd take that to heart.
Apart from that, I have suspicions that there might be something in your resume or cover letters throwing up red flags. Of course, it's hard to know if that's the case or what, in particular, is causing the issues without seeing the documents. In general, however, my recommendation would be to go back through your resume and cover letters and ensure that everything included is UX-oriented.
For instance, I see that you listed your background as being in "education, digital media, visual art, woodworking, and CAD design." Two of those-- digital media and visual arts-- jump out at me as being possibly UX-related, and your CAD Design piece seems like it might have been as well. Unless you taught some sort of visual design class, that probably needs only a line or two. Ditto with woodworking.
A good approach to consider may be a skills-based resume, rather than the traditional experienced-based resume. This highlights what you can do, what you feel comfortable with, and where your strengths lie. These are also great for getting past the automated portion of resume weeders as they highlight key words and skills that automated programs look for before sending along a resume to a human being. Tutsplus has a pretty article on the topic, and Google can supply you with a ton of examples. If you aren't using this format, I'd give it a go with a few of your next few applications and see if it helps.
Most importantly, if you do nothing else, do not give up. Success in anything worth while does not come overnight. Your battle right now is one of your will against your skill. You're locked and loaded with skill, and now the world is testing your will. I know it's tough when you're doing all the right things, living like your dream, walking like your dream, surrounding yourself with your dream, making the investments. I know it's hard when you're doing all of this, and your mountain isn't moving, and nothing is happening yet.
Understand that the action of making progress is progress in itself. The push, the process, regardless of the outcome, is progress. If you keep giving your effort, if you keep that grind up, I promise you-- your mountain will move.
Life's just decided it has a little more challenge for you. Don't give up.
I hope that helps. Let me know if there's anything else I can do to give you a hand!