Matt,
Be careful what you say to yourself about yourself. What I see written there is some self limiting beliefs that have the annoying tendancy to become fact. At the same time I see evidence that what you said is not entirely true.
Obiously you can still think. May take you longer than you felt it used to but you're still doing it. You come back to this thread to talk the problem over. If your skills were really as poor as you say then you would not have bothered coming back. You are also diciplined enough to do SFQ on a daily basis. Therefore you have the discipline to carry through other things as well.
From what you've said so far your style of thinking has changed and in some ways you have distanced yourself from your thought emotionally based on a past experience. Fair enough. There are still some things you can try.
You could look for ways to use your skills, the way your mind works now and seek new horizons. Perhaps you can find a breakthrough in a skill like art, sculpturing, model making, bonsai.
You could also try belief modification. You pointed out that you have an area in your life that may have triggered the problem for you. Well the Belief paraliminal can help you modify the limitations of that belief. There are other techniques to. Like rebuilding your self confidence. See humour in it. 
Letting go of the fact that your brother is a world class... and no one else wants to see it. It only makes you feel lousy like the guy who had dinner with the alien from the planet xenxue and they ate diuqs with storrac, snaeb, and nroc. You don't really care right? Really how important is it?
Sorry if this post seems to lack in clarity. I just came back from dealing with a Government department and am in awe (being extremely polite when I say that) of their supreme efficiency (actually it's brilliantly stupid) in tying another knot into their Gordian knot of red tape.
Anyway Matt, you might just have to start by changing your beliefs. Hang in there. There'll be more ideas coming I'm sure.
AlexK
