We've used the bar analogy a lot and when I stop and think about it, I've always left my favorite bars after a while because the vibe changes as new regulars populate the place. I feel like if there were a few such places on the internet where I could go and bump into familiar usernames, I'd feel less annoyed by influxes. I don't think that any of us wants to feel that we have to maintain anything, especially for something we're doing in our free time. For me, over the past few influxes hubski has started to feel more like a chore.
For it to continue. In real life this is done through things like tradition, common history, food, language and family. Other than, "welcome to hubski! did you check the primer page?" and "lurk moar!" what can we do? Take everyone by the hand and show them how we've been doing things? Sounds exhausting to me, but cheers to anyone who has been trying to maintain the site culture.
Keep participating. Welcome people who are doing it right. Give the cold shoulder to people who are doing it wrong. Don't feed the trolls. Eventually some people decide this isn't the community for them, some decide this is the community for them, and the trolls realize they're foaming at mouth in an empty room. It's a fragile thing and stops working if an overwhelming number of people want to come recreate reddit, but I don't think we're anywhere near that point.