Well my feelings on 'about' pages are that to some extent, they can offer the surfer a feeling of transparency, letting them know there actually is a 'real' person behind a site, at the same time, they can also be good for sites that require some kind of personality on them to excite the surfer a little more than just the tour or main sites content would.

With niches specifically id imagine that if you could create an 'about' page telling the surfer how much you love a specific niche, they would be more inclined to join a site that you reccomend, i think these types of pages would work a lot better on regular updated blogs that dont utilize RSS feeds specifically or hub sites/directories.

Regards,

Lee