Yeah, waterfalls are tricky. Probably the best application of it in forced perspective is on Radiator Springs Racers, and that's largely because it's only meant to be few hundred feet away (unlike these mountains that are supposed to look thousands of feet high) and you only have a few seconds to look at it.
As far as the tree canopy, not much we can do but wait. Just have to give it 5-7 years for things to grow in. I remember my family being quite surprised at how much the tree canopy had grown at AK from out first visit in 1998 to our next one in 2005. It made a huge difference in the appearance and atmosphere of the park, especially in the Oasis and along the animal viewing trails.
The banshee ride is still a bit of an enigma. It's hard to tell from the video, but the setting looked a lot like Soarin', with benches stretching across the theater. Hopefully it's a bit more intimate/unique in person.