I'm in a campaign that happens to include the brainer, and two things that have been noted as common came up: one, she was a little detached from the rest of the group whereas the rest of the group had a very thick web going (admittedly, the brainer kind of lends itself to that), and two, she took the violation glove. She's not still detached--she put herself out there, took risks, acted on and spoke about what she's passionate about--and she's getting closer to the other characters as a consequence of these things.
That said, I don't think the brainer is there for people who want to be detached from their own characters. Hell, you could do that with any of'em--and the brainer is not necessarily that hard to relate to, but I speak as someone who, if asked to generate myself in Apoc World, would go brainer. They're unusual, sure, but if you look past the creepy psychic powers, they represent someone who's really out there: someone who's introverted, who maybe didn't have the best social skills on the surface when they were growing up or perhaps even today, but these days, even watching and learning from the outside, they've come to understand people. Their distance lets them see the things that people who are closer would miss due to emotional attachment or because the person being observed shows closer people some other side of themselves. Their ability to step back and see people as they are rather than as they want to see them gives them understanding that the more emotionally invested would not want to have. Also the words "GET OUT OF MY HEAD" are the funnest words to hear, no shit; that moment when someone realizes that you're telling them exactly what they're thinking is a blast. Of course in real life I can only torment my inner circle with it, but hey.
Or maybe some people just want to play the creepy psychic stalker weirdo who watches people sleep. To each their own.