Technically, the AAA Diamond parking is for people who have booked an all-inclusive package through AAA. Oddly enough, at Epcot we discovered that AAA lot is shared with the Kennel Club (i.e. same lot for both). Wierd.
Anyway, the reserved parking spots are very convenient, close enough that you don't need to take the tram. Recommended for the stroller crowd if you don't want to have to break down your stroller to get on the parking lot trams.