We just got back from a week at Azul Sensatori in Mexico. We don't have a lot of experience with AI resorts, and the first time we went we had a bad experience. Unfortunately for us, the resort was closing up a few days after we checked out. With that in mind, we tried the Azul resort over winter break. You can read my Trip Advisor review here:
http://www.tripadvisor.com/ShowUserReviews-g240327-d1176806-r246695762-Azul_Sensatori_Hotel_by_Karisma-Puerto_Morelos_Yucatan_Peninsula.html#CHECK_RATES_CONT
Now, everyone likes different things and expects/wants different things. For what it's worth, we're not big on AI resorts because:
1. We don't eat or drink enough to make up for the AI fee. When we go on vacation, we don't cook in the room at all. We eat out every lunch and dinner, with an occasional breakfast. Even with that, along with the drinks on the beach and at the pool, we don't spend nearly as much as what the AI fee is. Now, that's a personal thing; since we're not big eaters and drinkers, it doesn't make sense for us.
2. I've heard (don't have a lot of experience) that most AI resorts have buffet restaurants. I hate buffets. It's not the "cleanliness thing"; I used to be in the restaurant business and it's incredibly difficult to do a buffet right. Most of the time either the stuff is glazed over from the heat lamps, overcooked on the bottom from the heat or just plain sloppy from people spilling stuff all over the place. We prefer quality over quantity, which typically you don't get at a buffet. This feeling about buffets is reinforced when we cruise (only done it 4 times, but consistently bad buffets).
3. When you exchange, the AI fee is based on the time of year you pay. We went away winter break, so our AI fee was significantly higher than the rest of the year (with the exception of new year's week). Now I understand that when you just book the room, the rate is based on the demand, however, since I own a week someplace and an owner of their resort also owns and we simply exchanged (all be it via II), it still bothers me.
4. We like to travel around the area, and with an AI fee, in the back of your mind, you say "well, I paid for it, so I mind as well use it". That's also the mentality of some people who go to AI resorts, "I paid for it, so I'm gonna eat and drink myself silly".
Now, for the "it's cheaper to book directly" issue. I'm a closet analytic and keep track of our trades. If we were to book our winter break at the Azul Sensatori, our total cost for the week would have been $7,642. The cost for our exchange was our maintenance fee ($1,345), our exchange fee ($154) and our AI fee ($3,031). So our total cost was $4,530, and as a result, we did end up saving about $2,100. Not a bad trade.
So, in summary for us, AI resorts don't make sense. However, in some areas, it's not easy to get into town for lunch or dinner (ie: Azul Sensatori), so if you want to go, you have no other choice. Other people may and probably will disagree and that's OK; it works for them.