Agreed, we used our AAA card a fair bit at US/IoA, probably saved...$50? But I also use it through the year for other hotel discounts (most chains you can get 10%, sometimes better) AND this year I got two jump-starts (dang kids leaving the doors open/lights on!) and a tow out of a snowbank. I also get their maps and triptiks when we travel. (The tour books are pretty lame IMO, but a map's a map.) I wouldn't buy it just for that discount, but overall for travel services and perks, I get a lot of value out of it in a year.
If you have a souvenier/restaurant budget, think, 10% or a little less, as we never remember to show it every time, and the carts usually don't accept it--stores and actual restaurants only. I believe it's the same discount you get with the AP, so if you have one of those, AAA doesn't add anything.