The need for helmets isn’t just to keep you alive; it may help you recover damages for injuries to the head. Wearing your helmet may not be the deciding factor to your injury claim, but it shows you’re a responsible motorcyclist. It could also indicate the negligence of the other driver. Insurance companies may also take helmet use into consideration. For example, if you were not wearing a helmet and sustained injuries during an accident, you may have to prove to the insurer that you would still have been injured even with a helmet.
The Mexican government requires that tourists get auto liability insurance from a Mexico-based insurance company. Although your USAA auto policy may provide limited coverage for any loss or damage that occurs within a certain distance from the U.S.-Mexico border (check your policy for details), it doesn't provide the insurance legally required for travel in Mexico.