what made Walt special

Watching Three Minutes, when Miss Klugh is asking Michael about Walt. She asks if Walt has ever appeared somewhere he wasn't supposed to be. We see multiple instances of Walt doing so over the course of the series. So he has the ability of astral projection. This is understandably something the Others would want to study, and ultimately use for their own benefit. We see enough through the series that it seems they don't truly lack for good means of travel, they seem to be able to arrange what they want quickly, and usually with some frills. Who knows, maybe they can teleport. But they'd certainly be interested in having an Other within the ranks who could just do astral projection, they could take care of more business that way