You cannot stack discounts, so because the 4/3 offer is a discount, there is no additional AAA discount on top of it. However, if you're going at a time when there are no such discounts, then AAA is often the only "deal" you can get.
Also, as previously mentioned, AAA does give you some perks including shopping discount at DTD, preferred parking, and the Storytime in MK (which is nice if you have little ones).