Currently, the comment for which I've received the most positive karma by a factor of four is a joke about institutionalized ass-rape. A secondhand joke, effectively a quote with no source cited. Furthermore, the comment had, at best, tangential relevance to the subject of discussion. If anyone were to provide a detailed explanation of why they voted as they did, I predict that I would be appreciative.
Based on this evidence, which priors need to be adjusted? Discuss.
"Worthy?" If that is defined by positive or negative karma, then yes, it is not worthy. However, when you want an answer to a question and are willing to lose karma for it, the current incentives are for making a top level post rather than an open thread comment, as long as you can deal with the people making meta comments...
I would say that karma measures the community's aggregate perception of worthiness, but does not define worthiness. My personal perception of worthiness reflects on the importance of the topic and the quality and novelty of the contribution to that topic.