Wasn't Obi-Wan Kenobi Supposed to Become Super Powerful Once Darth Vader Killed Him?
In the first film of the Star Wars saga, A New Hope (Episode IV), Obi-Wan Kenobi tells Darth Vader that he is going to become more powerful than what Darth Vader's imagination holds. In his exact words, Kenobi says, "You can't win Darth, if you strike me down I will become more powerful than you can possibly imagine."
This occurs when Kenobi meets Vader for their last duel inside the first Death Star built by the Empire. Of course, Vader wins the duel because Kenobi lets his guard down. Why he let his guard down? Well, in the movie Kenobi let Vader strike him down so Luke Skywalker and the gang get away on the Millennium Falcon. How did that exactly work? I don't know, but Kenobi sure let himself get killed for practically nothing.
Anyway, Vader takes out Kenobi by slashing through the torso. However, instead of getting Kenobi cut in half, his body simply vanishes into thin air. His threat of becoming super powerful was showing some promise at this point.
Luke screams for Kenobi as he witnesses his short-term Jedi master lose a fight by forfeit. I mean, C'mon! Anyway, Luke and the gang get away and join the Rebels as they had rescued Princess Leia from the Death Star.
It is when Luke attacks the Death Star with the X-wing squadron that he is contacted by Kenobi. Luke hears Kenobi's voice, "Use the Force Luke", which gives Luke hope and takes the lucky shot that destroys the Death Star.
At this point, Kenobi's power is indeed pretty powerful because he is talking from the dead. It is later in the sequel, The Empire Strikes Back (Episode V), that Kenobi's spirit is seen. Apparently, Kenobi's spirit has been training Luke for some time between episode IV and V.
Despite coming back from the dead as a neon colored spirit and having the ability to contact Luke, Kenobi's powers do not really become stronger. In fact, Kenobi cannot even finish training Luke into becoming a Jedi. He sends Luke to see Yoda to complete the training.
In the end, Kenobi's powers do not become better. He simply becomes an entity that can have a conversation. When he told Vader that he was going to become more powerful than the imagination can hold, he made it sound like he was going to be a force to reckon with.
It turns out that he just simply gains the power to train Luke and that is it. Seriously! If he was super powerful after death, he could have helped Luke fight that damn snow monster at Hoth. Kenobi could have also fought the Empire as a ghost. I mean really! Instead, his ghost just gave instructions and had tea with Yoda all the time!