I think we all know why movie-based attractions are good for business. People already have a connection to them, and it makes them want to visit the park, just so they can "live the movie." (Indeed, I want to go to Universal's Islands of Adventure to enter the world of Harry Potter). Their presence also cross promotes other movie-related products.
Walt knew this too. This is why the Disney classics had their home in Fantasyland, and ties to other Disney properties, such as the True-Life Adventures in Adventureland, were also made.
Walt gave the public what they expected. People do expect to see Disney film properties in a Disney park, and this was just one of many problems with DCA 1.0. HOWEVER, Walt also gave the public more than they expected, which is why, from Day One, there have been attractions that were not based on any specific Disney movie, but stood on their own.
I don't think anybody thinks that Disney should stop making movie-based attractions. But I'm here to say that original attractions can also be good for business.
The classic non-movie-based attractions of Disneyland are just as identified with "Disneyness" as any movie or TV show. In the beginning, they were designed by some of the same artists that worked at the movie studio. They are not esoteric, inaccessible cult classics, liked only by obsessive fans, (as they are sometimes portrayed.) Most were wildly popular when they were unveiled, and several remain popular decades later.
They feature original music, including "In the Tiki Tiki Tiki Tiki Tiki Room", "Yo Ho Yo Ho (A Pirates Life for Me)", "Grim Grinning Ghosts" and of course, "it's a small world". Everyone knows these songs. Numerous albums have been sold.
These attractions helped Disneyland establish its identity as an entertainment entity in its own right, which, I believe, is one of the reasons it's so synonymous with the quality theme park experience, and enjoys such popularity today, and why other parks which attempt to lure guests in with well-known properties are not always as successful. The popularity of Pirates the ride is surely what led to the greenlighting of Pirates the movie, since pirate films were considered dead in the water at that point. And that became a huge cash cow for Disney.
Attractions like Pirates and HM captured the essence of subjects that held a prominent place in the popular consciousness. This is why Soarin' is so popular – because people everywhere dream of flying. And this is why Soarin' got cloned at Epcot, and I've read it's very popular there, too.
If DCA wants to establish its own identity as a full-fledged theme park, what would help do so better than a distinct-to-DCA original E-ticket – an immersive ride with the detail of Pirates or HM – that would say, "this is what DCA is all about."
It also helped that, even as late as the mid-90's, movie-based attractions were approached much more like originals, putting the guest at the center of the adventure, focusing on atmosphere and setting, rather than pushing marketable characters. I hope that this will be the case with The Little Mermaid and Radiator Springs Racers.
And lastly...if you've got some of the most creative people in the world on staff, it seems like kind of a waste if you don't at least give them a shot at creating something original. From Mickey Mouse to Star Wars, everything that's popular today was once an unknown new thing that somebody had to take a chance on making. And you never know what the Imagineers might come up with, given the chance to go truly "blue sky", instead of being locked in the "blue sky cellar" . I also think Pixar should have a shot at developing an original attraction, the way Walt's studio artists did back in the day. You could promote it as "from the makers of Toy Story and Finding Nemo, comes an all-new adventure that can only be experienced at the Disneyland Resort!"