Peter Pan's Flight doesn't need to be expanded, just cleaned up with new effects added.
And as you mention Philharmagic, there's an attraction that could be expanded. A new sequence based on another Disney classic would be great. Adding it shouldn't be terribly difficult, and such a sequence could be removed during busier times when capacity becomes an issue.
I entirely agree. In fact, I'd go a step or three further. Create scenes from another 3 or 4 classics, and put a little randomization into the sequencing, so you don't know exactly which scense you'll see. Some of the transitions (e.g., Fantasia into Little Mermaid) can't really be changed, but others certainly could be.