I think Reddit (and HN) should make votes and ip addresses transparent for external analysis. The spammers hide behind these.
They could also be more brutal with punishments, route every single link to the offending site through a page that says they were spamming so it's an inconvenience for people and a wall for search engines.
ah, that might work, if users can't be tied to upvotes, just that one upvote can be tied to others. Still, if someone finds a way to associate a username to a hash, then there could be real life consequences for that.
It doesn't have to be a reversible hash, just assign a guid for each ip address.
There are probably subreddits where that information could be potentially harmful (eg upvotes in jailbait way back when) but that can be solved by not enabling it across the board, and it's not an issue here. Digg made their upvotes public from the start, and so do delicious, facebook, stumbleupon etc.
They could also be more brutal with punishments, route every single link to the offending site through a page that says they were spamming so it's an inconvenience for people and a wall for search engines.