Is the point of karma to provide feedback to the poster or the potential audience? It seems like these are both being used to determine whether to upvote. Maybe there should be explicit;y separate karma scores for different goals.

Perhaps posts should be evaluated on more comprehensive criteria: Helpful to me Relative value compared to other posts Feedback on post quality to author

I'm not really sure where the line is between not enough things to rate and too many though. But I've never been comfortable with single number systems.