Do we really want people chasing karma on here? I'd be tempted to go the other way, and limit the visibility and usefulness of it. I.e., on user profiles just show "between 1-50 karma", "500+ karma".
This also seems like one of those things where Goodhart's law may apply.
As a corollary to my point, we'd also like thought-provoking material rather than pure provocateurs. But I'd take an intelligent provocateur over a philosophically/historically uninformed HN comment any day of the week.
As this brief discussion of the HN metagame shows, anything that gets a number stuck next to it will attract people to optimizing it like flies to a manure pile...
Mostly I upvote if the user posted interesting/useful information.
Sometimes I upvote things I disagree with if I think it promotes a good discussion.
The utility of it as a means of operant conditioning and positive behavioral reinforcement can be debated (personally, I wish it would be done away with) but chasing karma is already a part of the site.