This thread really has nothing to do with SPG specifically as Hilton, Marriott and most chains offer AAA discounts.

To answer your question, I think AAA membership is worthwhile if you drive a car and might need roadside assistance. I have called AAA to start a dead battery, fix a flat and tow a vehicle. All of these services saved me time and in some cases a great deal of inconvenience. For example I damaged my rental car about 100km outside Vancouver. The rental car company insisted that I have the vehicle towed back to the airport. We have AAA+ (an additional $25) which covers 100mi of towing. So we called AAA which arranged for a free tow (and a convenient lift back to the airport).

AAA membership gets you pretty much the same perks as SPG Gold, minus the bonus points. That could be another plus depending on your status.

As for discounts, I find most of them worthless as I can usually get better hotel rates on priceline or with other discount codes, but YMMV.

In sum I endorse AAA for the peace of mind, particularly if you or your loved ones need roadside service at night. However, if you are a single guy who doesn't mind changing his own tires or doesn't drive far from home, then maybe it would be a waste.