Communities and Stuff

I see a lot of communities I'd be interested in joining, but many of them haven't had any activity in several years. Is there a point in trying to revive, dare I say necro, an old community, or would it be better to just start a new one from scratch?

I mean, maybe old communities could be revived if a lot more people come over here from Tumblr, but I'm just trying to get a grasp on the local etiquette.