Sounds like you're right about them buying mailing lists, though I suspect they try to buy ones where the people on them are generally of the right age. Otherwise, I'd have been getting their ads for years.
Re discounts, I have AAA and haven't found their discounts to be so great. I've used them for hotels, but most hotels will give you a better discount for almost any other reason (low occupancy that night, being in the military - and they will sign you up for the duration of your stay if you're not, can't even think of all the alternate reasons that got bigger discounts than AAA). Some, when they are too full, feel they have the right to refuse the AAA discount. It does come in handy at tourist attractions. They have good discounts for online stores, but I rarely shop online.
While I'm ripping into AAA, I was very unhappy when I renewed this year. I buy the premium level plan, so I can be towed up to 100 miles if I need it. Not that I've ever needed to be towed more than 3 miles, and that only twice in all the years I've had AAA, but I'm paying the $100/year just in case. So I was really unhappy when the woman said, "That gives you up to four tows for the year." Huh? I'd thought it gave me unlimited tows for the year. Again, not that I expect to need it, but if that's all I get, maybe I won't bother renewing next year. Compare the cost of one tow every several years with yearly premiums. My car insurance includes tows for accidents, and my tires have some kind of inner structure so I can drive on them when they're flat. So maybe I wasted the $100...
AARP's premium is a lot cheaper.