These days, unfortunately, are likely over. The benefit of the parks is the opportunity to sell to a captive audience the other Disney properties. As Disney has become a much larger media and IP giant, having a captive audience to essentially pay you to spend multiple days being advertised to is too hard to pass up. While Walt and his followers may have seen the parks as a differentiated part of the Disney family, something to be invested in as a stand-alone, that is (seemingly) no longer true.
Now, the parks seem to be seen as what they probably should be in the mind of a large corporation - a media outlet and direct connection to the consumer. Keeping the Disney IP library in front of milions of local and international tourists each year help sell those properties in their other formats (movies, merchandise, plays, etc.).
I don't think that will change as unfortunate as we may think it is.
We certainly saw shades of that during the 90s, as well (think back to all the ABC show signs all over MGM Studios after the Capital Cities purchase), but yeah, it definitely has grown. What I think I'm most curious about is how effective that will prove to be over the long haul versus the creation of more unique attractions.
I mean, Disney characters have always been used on some level to sell the concept of a Disney theme park; if not, they wouldn't have had costumed characters appearing right from the get-go in 1955. Yet the parks themselves for most of their existence seemed to use the characters as a lure, but really hook people in via the unmatched theming and unique creations from WED/WDI, though there was still always a place at the table for meeting the characters or riding some movie-themed rides like Peter Pan or Snow White. It was this aspect, the more creative aspect, I'd argue, that created the lifelong Disney theme park fans, the type of people who visit Disneyland every weekend or who set their vacation calendars around arriving in Orlando at least once a year, and who think "I HAVE to share this with my kids in the future". The familiar was used to market and support the unfamiliar, but the unfamiliar was what wound up having the longest lasting impact, if that makes any sense.
Now it seems to be the other way around: the parks are the lure to get you to...see movies that Disney owns? I don't know, it seems flipped to me. Most people already know what Star Wars, Marvel, and the animated films all are, and a trip to the parks isn't likely to get a big time new audience drawn to them, but rather just reinforce the pre-existing audience. One can certainly commodify that pre-existing audience if the fanbase for a given property is large and rabid enough (again, see Wizarding World), and I could easily be wrong about this, but I have a hard time seeing a film like Frozen or Finding Nemo attracting bigger audiences than they already have based on their EPCOT attractions. In other words, the people that are likely to see the movies Disney owns are the people already booking trips to Disney theme parks, so outside of selling certain merchandise at the gift shops (a lot of which is already available at your local mall's Disney Store or online), I don't think you're doing much to grow your prospective audience. So now the unfamiliar is being used in service of the familiar, which already is about as big as it's going to be.
Again, I'm curious to see how well this holds up over time. Do less parents feel enthused about bringing the kids down to Disney because "we already have to watch that DVD too often", maybe because they feel less of a connection to the material that's drawing the kids in (don't forget: there used to be a lot of cross-generational appeal back in the days when Disney would re-release older films into theaters, so kids, parents, and even grandparents often knew about Snow White, Peter Pan, Mr. Toad, Alice, et. al.)? Does the potential loss of consistent theming leave kids less likely to feel that sort of subconscious pull that says "I want to go back to that place" even after they've outgrown some of the stuff they may have liked as grade schoolers? What about kids who aren't lining up to be superheroes/pirates/princesses, a group Disney did used to hold a lot of appeal with? Or does WDI come through and ensure that it works out, and corporate comes through to ensure that the parks aren't just dealing with overlays and no expansion in the actual number of attractions, and we get something stronger? Just so may questions.