You're overstating this, I think. How much would a downvoting HN account be worth, really? Sure, a spammer could sneak in a few messages at a more visible lev

You're overstating this, I think. How much would a downvoting HN account be worth, really? Sure, a spammer could sneak in a few messages at a more visible level, or presumably down-vote their competitors, but the suddenly-abusive account would get shut down pretty swiftly. On other hand, the work required to get an account up to a significant level (say, 500+) is non-trivial, cannot be outsourced to a minimally-trained mouse-clicker, and wouldn't run cheap. It's not clear to me how it would help a spammer to know what the limit it, given that it's high enough that the work is not worthwhile.