Question: How was Obi-Wan going to become more powerful after he was dead?
Answer: I agree with Darius Angel's comment. I also think Vader expected a certain sense of satisfaction after defeating his former master. In reality, though, he was still "owned" by the Emperor and was living with the consequences of his choices. Defeating Obi-wan did not change much for him. Obi-wan, however, gained the benefits that Darius Angel mentioned.
Question: How is Elliott spelt, as I've seen it both Elliot and Elliott on various different Disney memorabilia?
Answer: In the original film, the credits show his name as "Elliott" (with 2 t's). In the remake, his name is "Elliot" (with 1 t). So older memorabilia will have "Elliott". In the original film, Elliott was the dragon's given name, in a manner of speaking. In the remake, Pete names the dragon after the puppy from his favorite book which was called "Elliot Gets Lost". This is the only reason I can find for the spelling change.
Question: Why were the aliens abducting people and why did they bring them back?
Answer: It wasn't definitively answered, but it appears the aliens took people in order to learn more about humans. It's unclear if all those who were returned had originally gone willingly, but the intent was not to keep them indefinitely or harm them, and they were returned to Earth, albeit many decades later. At the end, after the aliens had made contact, a new group of humans, including Roy, went with them voluntarily.
Question: Has there ever been a backstory written for Jaws? I would love to know where he came from, and how he came to be, so I was wondering if there has ever been one written, and where I can find it.
Chosen answer: Yes, there was a backstory for the character of Jaws in Christopher Wood's novelisation of the film "James Bond, The Spy Who Loved Me", not to be confused with the Ian Fleming novel.
Question: When Michelle Stacy played Penny in the making of the film, did she pose for the drawings of Penny? Did Stacy even have to hang upside down in order to pose for the drawing of Penny held upside down by Brutus?
Chosen answer: As amusing as that would be, 99.9% chance she was not hung upside down from her undergarments.
Answer: It is heavily implied that one who becomes a Force-Ghost achieves an untold level of power upon entering the state. Given that they have become a pure entity of the Force, it seems to back up the statement. Obi-Wan also becomes free to assist Luke in any case.
Darius Angel
In addition to this answer, I think Obi-wan also became powerful because he "let go." He did not feel a need to defeat Vader on this occasion - he was willing to surrender the fight and "move on" to a new state. Something that Vader might not currently understand.