I don't autocross, but this started to happen to me so I bent the pedal up about a year ago. 6 months ago, it was doing it again and I noticed the pedal bent back up much easier that time. Pretty sure the pedal arm is weakened so I ordered a new gas pedal from Mazda and I'm pretty sure it was like $20, and it's on the list of things to replace while my engine is out.
I'm no welder, but I bet the arm can be significantly strengthened by welding on a couple .125" steel strips on whatever section is bending the worst.