The vision is easy to maintain mentally as it is pretty clear (although many see what is "Disney" very differently), it's finding a way to achieve that vision (or essence) within the business and public restraints that exist in today's world. Walt maintained his vision because he ran the place. When you are a "Cog" in a big machine that has quarterly needs, even a powerful "Cog" has to conform to goals that are sometimes counter to the vision and mission of the Man Walt Disney versus the brand Walt Disney. In the 70's it used to be "Look to the name Walt Disney for the finest in Family Entertainment". Not sure that's where they are headed or want to be anymore. Maybe that's one reason they dropped the "Walt" from the "Disney" brand in movies as they don't want to be restrained by his image and perception, or his moral compass of personal ideals.
I try and keep the Disney vision today even though I don't work there. I still believe in the quality, creativity, and kindling the upbuilding nature found in making people feel good about themselves and who they could be. As John Hench said, it's "reassurance", something this world provides very little of. To me, "every guest is still a VIP" on any project. Dignify everyone with a great experience. Any project should be approached by appealing to your better nature, not your baser instincts. Deliver honest emotions by designing from the same place. If you are "people driven" you won't have to be "profit driven". Give them more than they expect and dream of what they cannot imagine, and build that dream a little better than you thought you could. To me that process breeds success and trust. That is why the Disney brand is still around despite all the creative abuses and mismanagement, it has endured for the last few decades because it had that foundation.