I guess the new user should be given a fixed amount of points (my suggestion: one.) to use them on posts within "happily closed" threads.


Besides that, to encourage people to post more often, I think the karma score should have limited lifetime. Say - every karma point expires after 3 or 6 months. This way people with very long stage won't be accumulating insane amount of karma, people who leave the forum won't take up place on the "high karma" list (not because they don't deserve but because the list is a great help in checking if the person replying to your post is reliable and the suggested solution can be trusted) and allow awarding those who post good posts more often.
(please disregard this idea if you think it's stupid)