Banning a single site feels good, but is a short-term band-aid on the moderation system. Better to identify the factors in valleywag stories that are undesireable and find a way to target them generally - to raise the editorial quality here across the board and leave behind the dross.
As others have pointed out, Valleywag doesn't have a monopoly on linkbait titles and thin follow-through.
Agreed, I think the important thing is raising quality across the board. Two possible solutions:
a) stop people voting for crap b) get the community to filter out crap.
I don't have any good ideas for option a), and I dislike reddit-style downvoting for option b) since it has the same problem of people upvoting bad stuff, just in reverse.
One idea which could work for b) is a digg-like 'bury' option (i.e. a 'this is crap' button) - but only in tandem with a high karma minimum for being allowed to use it, and some statistical cleverness for deciding when a post should be buried. But I'm terribly enthused with this idea either.
How about time-regulated voting for a)? ( see http://news.ycombinator.com/item?id=147383 ) Presumably, people who go on an impulse voting spree do it without much thought and would be greatly discouraged by periodic voting prevention, whereas those who take the time to make thoughtful votes and comments wouldn't mind the regulation as much.