Well i guess about Anakin's ghost in the end of ROTJ original version, is because he was the greatest jedi and sith ever lived. He was the one to destroy the sith and he really did it as jedi knight and aslo as dark lord of the Sith, by understanding his own son's pain. As Padme said to Kenobi "there's still good in him" yes of the point of view of someone who is in a relationship with him, in marriage and is the mother of his kids, she knew him better even than Master Kenobi. As father Anakin/Vader himself, even as the most iconic evil figure of all times, he is still touched by the emotional even spiritual (if you want) bound between him and his own flesh and blood - Luke. That is for me the reason to turn against his twisted evil master the Emperor, and by that he realized how much bad he have created in the universe. There is a redemption for sure. And by killing him he returned the balance in the Force as it was told. It could be a reason why we would see him as force ghost in the end, by that he reached a higher level of the force, assuming no one until than has ever returned from the dark side. As Master Yoda told Luke and not only him, once in the dark there is no coming back, but Anakin managed to do it after all. And don't forget that in Episode 3 he might be a young Jedi Knight around 20-30 who leave 2 babies, but when the time come of the New Hope to rise as his own son was near the same age, that was years later and it is normal to see old Anakin in the end. Personally now i am a little bit interested in the story with Darth Tenebrous, since it is very possible he's the real father of Anakin and not just Darth Plagueis. In fact it can be Tenebrous reborn..ed from the maxichlorians as a powerful boy named Anakin