Newsflash, Disney is not an omnipotent superpower. They are a corporation, run by people, capable of errors, both in execution and judgement. How many Disney projects have been abandoned AFTER their public announcement, which means long (like YEARS long) after their private planning has been assessed, approved and begun to be executed? What looks good on paper doesn't always pan out in the real word. Projected gains, predictions of future behavior, profit projections: all are extremely fallible ... In both directions.
Disney most assuredly does NOT know more about my family our your family than you, or I, do ... Not in the sense of the collective, nor the individual "you." To think they do is blind worship and, frankly, a tad creepy.
Historically company's expectations of micro marketing and targeted consumer data mining's translation to actual real profits have been wildly overblown (witness basically the entire tech bubble for examples). It's too soon to tell if this is the case in Disney's instance, but it would hardly be an unlikely outcome.
I in no way, shape or form believe MyMagic and FastPass+ will bankrupt Disney, ruin the parks or wildly effect overall attendance (in either direction), I just don't believe they will ever prove "worth" the cost paid for Disney's bottom line. Based on Disney precedent, I think they'll eventually get the system working reasonably well (scrap parts that don't work at all, improve the tech reliability and modify the system to please more patrons) but I still think this will go down in history as a financial boondoggle that never, ever pays off as originally projected (meaning: in the way they foolishly forecasted when they chose to devote funds to this versus other projects, namely expansions).
On the other hand, infrastructure investment, as proven by Universal and Disney's own California park, can provide serious and almost guaranteed return on investment pretty much immediately. From what I've heard/read both Universal and Disney California recouped their capital improvement investments within 12 months, which is a freaking awesome return. Not only would it have been better for consumers, but the smart money at Disney would have been in and, honestly, still is, adding additional rides, lands and gates to their park. History has shown that if they build it, people will come.