I've been asked for the card on occasion, a couple of places actually enter the numter into the reservation to confirm they saw the card. One (think it was a Hampton in Mass) said their audtors required proof of any discount cards or plans for the discount rate.

If you don't want to spend whatever your local AAA charges, and you are 50 or over, consider AARP, it's a bit less money, and the discount is close to the AAA one for hotels.