I see we're talking about movies now. But on the subject of a celebrity as Dreamfinder, I think it's a bad idea, as I do the injection of celebrities into other Disney attractions. First and foremost, seeing a celebrity in a Disney attraction takes me out of the Disney experience, and reminds me of the "real world". The Disney parks were created to be immersive environments where you could temporarily forget about the outside world; WDW takes this to the extreme even, by physically removing you from the outside world more than any other property.
For me, it's hard to see the celebrity as the "character" they're playing. I thought about that earlier, and wondered why. After all, I've seen Robin Williams in numerous movies, and accepted him as whatever character he was playing. Yet when I heard his voice as TimeKeeper, I couldn't get the image of Williams as Williams out of my mind. Likewise Phylicia Rashad in CTX/Dinosaur was Phylica Rashad (or Claire Huxtable) to me. I finally concluded two things: one, we're in a sense "trained" to accept actors playing different roles within the context of television or film. When you take them out of that context, it messes with my perception and bit, and causes me to think about the actor rather than the character. There's also less character development in Disney attractions, as there simply isn't the time, focus, and emotional investment that there is in film (or even TV). Conversely, we're trained not to expect the "real world" to encroach upon the Disney experience. So the effect is easily doubled.
The other problem with using celebrities, is that they quickly become dated. In college, I took a creative writing class, and one of the things that particularly stuck in my mind, was the instructor warning us against using elements that tied to the story to a specific time (unless it was a historical/period piece). For example, using faddish slang, referencing then-current technology, etc., would limit the lifespan of our work, by "dating" it with current-period references. Celebrities do the same to Disney attractions. The "flavor of the month" won't be the flavor of next month. Look how celebrity-centric Disney-MGM studios started out, and see how short that lasted. Anyone remember the Bette Midler film?
I think that if Dreamfinder returns, he should be allowed to be his own person, through and through, without carrying the baggage of celebrity.
G7