Sandy, for your $55 ($50 if bought ahead of time) you get the T-shirt, Hat, License plate and bag of donated stuff. You also get the window tag that lets you into the downtown area for the car show. Otherwise you will park farther away. Finally, you are supporting the Route 66 Assoc. of Arizona who runs the function. This is probably their only annual event.
http://www.azrt66.com/funrun.htm
Ultimately the answer is no, you don't. We will still love you.
AZ Bob