I think the big difference is that for the most part (excepting us theme park geeks!) most millenials don't have much concept of, or loyalty to, Walt Disney, and what the Disney company was in the 80s and 90s. What they do have, however, is a love for the characters and movies of the last 25 years, and that will keep them coming, *not* the company culture or the Disney difference that attracted generations in the past.
In the past Disney movies were only so-so popular, but the parks were attractive because the rides were better, everything was maintained well, there was no litter on the streets etc... now Disney movies are super popular, and it's the lure of meeting characters and nostalgia for the films that will keep people bringing their kids, regardless of whether the in-park culture and small details that appealed to previous generations are still there or not.