Headset rental for Nascar. Worth it?

Absolutely ! !
First one we went to, didn't get them at first, took about 30 lap at Vegas, went and got them.
It's so load you can't hear the loadspeakers most of the time, the headset allows you to hear the narrator. The narrator makes you aware of the leaders, cars trading paint, spins you wouldn't see, so it's way more than just listening to a car crew as you watch a buncha cars go in a circle, you actually get to know what's going on.
You can also plug a guest into your receiver. Monitor diff cars, crews.
Definitely would miss one aspect of the race, without them.
Have fun ! !

EDIT