When you get hit or fall, if you have your mouth open, the impact from your jaw slamming shut can actually cause a concussion. That's why fighters wear a mouth guard. It's not only to protect your teeth but to stop that force from your jaw slamming shut and literally knocking you out.
But I have a home in Havasu as well (no helmet law) I ALWAYS wear a helmet, wont ever ride without one, not worth the risk. Plus I am too aggressive to ride without but I am on a plated dirtbike and heading to the off-road spots anyway, where I am dressed head to toe in full gear at ALL times.
I still see tons of guys without them, but I used to work as a medic so I am all to aware of what a a fatal MVA motorcycle accident looks like, hard to forget seeing a skull capped victim laying on the ground with no other obvious trauma especially when it could have been prevented.
BTW I have BROKEN 3 helmets in my riding/racing career. If thats not a good enough reason, I dont know what is. IMO thats 3 extra lives!
So not worth it!!