Isn't this what the 'long tail' is about? Online, your 'neighborhoods' are demographic niches.
Now, if the needs of your online 'neighborhood' have already been met, then that's similar to living in a neighborhood full of Italian immigrants and still looking to start an Italian restaurant nearby. You'll have to move and learn about the needs of other 'neighborhoods'.
Many people (including Eric Schmidt in a submission that was posted earlier this week, although I've certainly heard it before) argue that the Internet follows more of a Zipf's Law distribution (http://en.wikipedia.org/wiki/Zipfs_law) than a "long tail". In other words, the bulk of the traffic and therefore the revenue is in the head. As a corollary, the Internet doesn't get rid of celebrities, it creates bigger celebrities.
Now, if the needs of your online 'neighborhood' have already been met, then that's similar to living in a neighborhood full of Italian immigrants and still looking to start an Italian restaurant nearby. You'll have to move and learn about the needs of other 'neighborhoods'.