First of all, very good post!
I have been fortunate enough not to hit any walls and unfortunate enough not to participate in any races thus far, but I can relate to you in regards to target fixation.
I have noticed sometimes that if my mind is not "right" that I am mentally telling myself to look through the turn and not at a specific object I would much rather avoid. If i am riding with a "clear" head it seems that everything just clicks and I can focus all of my mental energy on my riding.
The best thing to do is put everything on the back burner and concentrate on the job at hand. Your success (and safety) could very well depend on this. Of course, saying it is one thing and doing it is another