This is exactly right. Disney's whole premise is that encouraging people to plan their vacations months in advance leads to more time and $$$ spent in the parks. I don't plan months in advance. It's just my personal preference - I prefer to allow some spontaneity on vacation, to go to bed and say, "What do you feel like doing tomorrow?" - or even wake up that morning and do what we feel like doing. After all, it's a vacation!
As a result, since the Dining Plan has forced people to make ADRs months in advance, my dining on Disney property has gone WAY down. I can't get a reservation same day or a day or two in advance like I used to. So where I used to eat a sit-down meal on property 4-5 times during a 10-day trip, now I usually eat just 1-2. The rest of the time is counter service (if we're in a park) or a nice dinner off-property (if we really want a good meal). I do miss eating at Le Cellier and Tony's, so you can definitely say that my experience is now worse than it used to be. I accept that, it's my choice. But that's still the reality of the situation. Disney is certainly losing some revenue from me, but they seem to be making up for it from other people.
I fear MM+ may have a similar result. Will I ride Soarin' and TSMM more or less than before? I'm thinking probably a bit less, since I was unable to get same-day FPs for these attractions. We were able to get them for later in the week (and hit the standby line at park opening), so it worked ok for us... but still...
Interestingly, during a pretty busy time around Thanksgiving, Soarin' and TSMM were the only attractions where we had difficulty getting same or next-day FPs. Maybe this will get worse as the system rolls out, but I think it's more a symptom that there aren't enough hot attractions that are really in demand. Every time I see the FP queue for the teacups I chuckle.