I think the Karma value of a post is quite useful. The Karma value of a person is less so - it's a combination of how long they've been around, and how good their posts are considered to be. As long as you have enough Karma to post a main article if you want, you have enough Karma, imo. Having said that, I do take more notice of posts from people who I recognise, or have something of a track record. We'd lose that information if Karma became something else.

There is of course the well-known incentive of changing the relative probabilities of a good or bad singularity - you would think that ought to be enough for most people.... Actually it isn't - we tend to do things like less wrong in order to mix with a community of like-minded people. I think encouraging that aspect stands most chance of success.