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.
Currently, LWers get +1 karma for a comment upvote, and +10 karma for a main post upvote. But clearly, there are other valuable things LWers could do for the community besides writing comments and posts. Writing isn't everyone's forte. Why not award karma for doing productive non-writing things? It's probably not optimal that karma and the community status that comes with it are awarded only for the thing that myself and a few other people are good at. For example, I really wish LW could award karma to programmers for improving LW.
The challenge is doing it fairly, in a way that doesn't alienate too many people. But there might be a workable way to do this, so let's explore.
Perhaps tasks could be assigned karma award amounts by LW editors (Nesov, Eliezer, Louie, etc.), or even just one person who is appointed as the Karma Genie.
Examples: