We just got back from a 2 week trip. Not counting the ride photos, we have over 800 pictures. We did NOT stop at nearly every PP photographer, in fact, we didn't even stop for the big picture (the one in front of Spaceship Earth, Castle, Tree of Life, Hat) every day, we only did those a couple of times during the entire trip. We probably have an additional 50-100 ride photos.
We did do many character meals. HOWEVER, it isn't as if there are PP photographers walking around with the characters. We have a few pictures from before the meals for those.
We did do a lot of meet and greets, where they captured about 10-20 shots per greet.
We did BBB where we had over 50 pictures from the makeovers and over 50 pictures from the photo shoot afterwards (I did have 3 children who did the experience).
We did PL, but there were only around 10 photos per child.
I think if you are the type to get the ride photos, are intending to do many character meets (and don't want to have to get your camera ready every time so you can also participate), or intend to stop at a lot of the PP photographers intentionally MM is a good idea to purchase.
If you don't care for the ride photos, are not going to do character meets, and don't intend to stop to get your photo taken in front of the icons, then it is probably not a good deal for you.