I would prefer them to keep B&TB, I think it is such a great show, for a park attraction musical. Not too long, but still the story is pretty much told and all the high points/classic songs are hit upon. They could do a better job keeping the audience cool though, maybe more fans or creating some more airflow somehow. It gets really hot in there in the summer.
Little Mermaid was just okay to me, though that is a very good movie. I think replacing that with Tangled would be just fine. Maybe at some point they can re-work the show and find space in The Seas at Epcot. Just trying to think real quick, is there a live stage/musical type show at Epcot at this point?
These shows, and FotLK and Nemo at Animal Kingdom are a real treat, and add a great deal of entertainment to those parks (along with Muppets 3D/Bugs Life). If you're not attending these shows, you are missing out on a great deal of the park experience, I think, and it's a major reason why people think these are half days parks at most.
Not everything has to be a thrill ride to be enjoyable/entertaining.