This is a perennial question that has as many answers as people offering the answers.
I can give a dual perspective--looking back when I did my own AOW and now as an instructor.
My perspective as a student:
As others have mentioned, there are certain dives that operators will only allow you to do if you have the training. At one point early in my dive career I was interested in doing a night dive, but was told that I needed at least a night-diving class. So I signed up with a NAUI instructor for the individual class. When I had finished it, he suggested that with just a few more dives I could do the entire AOW cert. I had the time, the price was okay, so I was sold! My instructor chose the dives I would do--we did night, deep, nav, wreck, and search/recovery. None of them was especially well done. In fact, he doubled up the night + wreck into a single dive, and he just threw a brightly-colored weightbelt off the back of the boat and told me to go get it for s/r. I remember having to learn something about tank construction, but can't recall which dive this might have been for, and since I wasn't given a book for the course (I did no reading at all nor watched any videos), I am at a total loss to explain why. All in all, I guess I'd have to say that my own AOW was fairly weak, but that I did learn some new skills like how to swim in a triangle with a compass. I never thought of it as a waste of time and money.
My perspective as an instructor: I'm sure that my so-so AOW course has influenced how I teach my own PADI AOW courses. No matter what level a student is at, it should be possible to take the student to a new level. For example, if a student is doing the Peak Performance Buoyancy class and has pretty decent control, the instructor could introduce techniques like variations on kicking such as frog kicks, finning backwards, hovering head-down, performing helicopter turns, etc. If on the other hand a student dives like a seahorse swims, the focus should be on the basics--getting him/her in trim, helping to put a stop to flailing hands, getting rid of bicycle kicks, etc. In other words, if an instructor is conscientious, just about any dive in the AOW can be made valuable to the student.
As far as curriculum goes, it's possible to select those dives that involve more skill development or those that are more experiential. Ideally, the student and the instructor will discuss which topics to cover in the course so that the diver gets real value, whether that means developing new skills or diving under new conditions. Where I work, the great majority of dives are done from boats, and yet I seldom include "boat diver" as one of the dives for AOW because most of my students have already done a number of boat dives and feel comfortable and confident about it. But I am more than happy to do "boat diver" if a quarry diver comes to me for AOW and is having his/her first ocean dive from a boat. Why not, if that's what will best serve the diver's needs? In other words, the AOW course can be what you make of it, if you are given the option to select which dives you want to do.
