So I obviously know nothing about this stuff but this is how I see it guys...
Spider-Man Ride = Really good quality = 4K
Soarin = Dated with scratches = film
And I'd say that's a fair assessment (barring the fact I've never seen Spider-Man) but the issue isn't that film is inherently the problem or that digital is an automatic improvement.
Digital doesn't have the same kinds of wear and tear issues that film does, so assuming that someone keeps the projectors focused digital should have a more
consistent image than film.
Where Disney isn't doing what they should be is in the area of
maintaining the film or replacing it as often as they should. I don't know what the average lifespan of a single print is, but I'm sure that having 24 - 30 showings
a day (compared to 5 - 7 showings a day for your average movie theater) really cuts down on how long each copy lasts. Multiply that by 9 for each Circle-Vision film, or three for Impressions de France, in addition to all of the other single-projector films on property and I'm sure it isn't an inconsequential cost.
Celluloid isn't cheap, and it isn't getting any cheaper, so changing to digital is a question of when, not if. I'd like to think that Disney knows very well where the state-of-the-art is in digital projection and is holding out for projectors that will be cost-effective and simple to run as possible before making the large investment required. I'm sure they've already done the cost analysis of replacement prints vs. digital transfer/projection which is why we're seeing the change coming on a theater by theater basis.
Of course, in the case of Soarin', the projectors required just aren't available yet so a changeover to digital is probably
at least a year off if not more.