The best possible scenario for trying to build web traffic is to have a lot of brand advocates who are passionate about the site. However, if I had to choose between a small group of people who really care about the site and visit it often and a large group of people who stop by once, maybe subscribe to a feed or newsletter, and rarely read my writing, I would absolutely choose the former. It goes back to that time-honored phrase, "take care of your people (in this case, your community members) and they will take care of the brand (in this case, the site)."
Now sites like Facebook are in that rare crossroads of having a lot of followers who are very passionate about the brand. I am one of them - I LOVE Facebook. I'm on there all the time, poking around, updating my status, emailing friends far and near. Most sites will never get that kind of traffic so they usually have to choose: lots of surface conversations or a small group of meaningful conversations?
Let's be realistic - my blog is never going to be Facebook. And that's fine - that's good, actually. I have a small group of readers that I love who read and comment on my writing regularly - some on my blog, some in person when I see them, some in very kind emails that they send me. They are extremely special people to me. I know a little bit, or a lot in some cases, about them and we have a good dialogue and exchange of ideas. If this blog were Facebook, I couldn't devote the time, care, attention, and honesty I do to the fun part - the writing. I'm one person writing about topics and people I care about. And that is a blessing to be able to do.