I would write a letter to AA, and cite an impending letter to the BBB. If you fly other routes or other airlines, I would cite that as the example for why you are not the problem, but rather the employee(s) on that route.

Aside from that, I would consider luggage insurance, such as the one offered from Amex, since they are really fast at paying for lost luggage, or at least that was my experience.

Rob