I agree with everything the OP said.
More interaction between Mufasa and Sarabi especially would have been lovely, as well as more Cub Nala (either more lines/extended scenes, or just some more interaction between her and Sarafina)
More of Mufasa teaching Simba what he needs to know about being king.
A little more mother-son interaction between Sarabi and Simba would have been good too.
Another thing I would have LOVED to see is Cub Nala returning to Pride Rock after the adventure at the Elephant Graveyard. I wonder how Sarafina would have reacted?