The new empire footage between vader and palpatine ruins the original ending of empire, because it is revealed earlier in the movie that vader is luke's father, so it wrecks the dark revelation "I AM YOUR FATHER!". The reason i'm saying this is imagine your seeing empire for the very first time, as their will be people doing being younger and newer to star wars, it gives away the ending of the movie making it anticlimatic. Not only that, originally we had to wait three years musing that vader lied to luke, only to find out the horrible revelation from yoda in jedi. The first movie IV made us trust obi-wan and like him, so we would be more willing to believe that old ben was telling the truth, and vader was lying. Revenge of the sith revealed that the jedi were all too willing to lie for their own agenda, and do immoral things to achieve their ends. Anakin was partially right that the jedi order was becoming corrupt, and after all he was being used for his gifts. So palpatine lied to him, a lie with a grain of truth.