Soarin' changes when the rides aren't two hours long most days. Star Tours changed cause hardly anyone was riding.
People say its an "easy" fix, but producing a new movie for Soarin would likely exceed $1 million. (remember, you have a large format film to be produced, ride mechanism, smells...etc.)
The funny thing is certain people ***** that "oh, that movie is old, they should change it." Well, if they changed it tomorrow, half the people would ***** "Oh, the old movie was so much better" and the other half 3 years later would ***** "Oh, I'm sick of this movie".
So, again, what's Disneys motivation. It won't bring more people into the park, and they'll get more whining for changing it than they do just keeping it the same.
I myself wish they would just get a new print of the existing film, its looking really raggedy.