Barriers to UGC adoption

I've been speak ing with a company about a potential UGC site and accompanying marketing campaign. One of the concerns is the potential lack of popularity of the service. They are well aware of the motto from the film Field of Dreams

"if you build it, they will come"

... and that this doesn't work for the web unless you have some mystic force supporting you.

Brian Oberkirch's post on 'Really, We Don’t Want to Join Your Social Network' puts forward the case (and well made it is is) for not building your own Social Network, especially when there's so many of them going up all the time.
With the bar to build a compelling community site rising all the time, its becomming very difficult now to stand-out from the crowd and its all looking a bit 'Me Too' isn't it?.

So has the door shut on this opportunity now?