My theory: Walt the Materializer
Ok, i have a theory about Walt and with this one i can give him a purpose on why the others wanted him so bad.
Scene one: Walt reading a book about birds and then BOOM! a bird appears out of nowhere.
Scene two: Walt reads a comic book about polar bears and BOOM! a polar bear appears in the middle of the jungle.
Scene three: The others kidnap Walt and state that he is special and they need him.
Scene four: Ben states to Locke that they have a MAGIC BOX that will bring anything you want to the island, no matter what it is.
Scene five: Ben takes Locke to a place and opens a closet, Locke's father appears before him.
Given the fact that no one really knows or has a theory about how the hell did Locke's father appeared, then i just gave you one.
Maybe Ben was using Walt as a materializer and used him to bring anything he needed to the island.
Can any of you think of anything else Ben could have brought to the island thanx to Walt??