Joel is right that you should always try to fix/improve/edit problem content first. However, if that's not possible for whatever reason, absolutely go ahead and downvote. While you're at it, raise a flag, too. Link-only answers are prime candidates for rapid mod deletion even when the links aren't dead. (Do give a full explanation of what's going on, though, so that the mod who handles your flag doesn't convert the post into an equally useless comment.)
More to your point, having a high-scoring post that contains little or no useful information doesn't help anyone, and it makes the community seem... let's just say "less than trustworthy." Perhaps the downvote will even get the attention of the OP and lead to an edit.