You should go for it if you can offer a compelling feature that facebook lacks. (I mean really really compelling). I think the advice about going at it oblique

You should go for it if you can offer a compelling feature that facebook lacks. (I mean really really compelling). I think the advice about going at it obliquely is only necessary if you're creating a straight up clone, this targeting a niche thing is only about marketing, but if you can offer something better, I think you'll find many early adopters.