As for my commenting, I can think of five basic classes of motivations:
I do consciously prefer the other types of motivation to the fourth one. One reason is that social signalling is already subconsciously the strongest motivator for participating in a discussion, and it may be preferable to compensate a bit. Standard debates all over the world are full of type-4 motivated contributions, and the results aren't optimal.
That isn't to say that we should omit social signalling at all, or that we shouldn't take care of the formulation of a comment or a post. Only that the signalling purposes should play a secondary role to the other motivations - if I want to ask a question or present an insight, I shouldn't refrain from doing so based on an expectation of being downvoted (there are situations when I should, but those are exceptions). Similarly, I shouldn't post a comment if the only motivation is to get upvotes.
There is a difference between communicating in a way approved by the community, and trying to communicating in order to get approval. If the latter was the norm, evaporative cooling of our opinions would become a serious danger. I was alerted mainly by this sentence present in the grand-parent comment:
If you care about karma, you're going to say wildly different things that you would otherwise. (emphasis mine)
Saying wildly different things for want of approval raises a particular red flag for me, and therefore I wanted a clarification. Not that I am innocent in this respect: although I respect people who are willing to sacrifice some karma when necessary, I can't remember of posting something controversial myself. Which I am a little worried about.
I consider this a low value post, because it muses about a particular idea without actually doing hard work to get it done. (I do not have the knowledge or resources to do so, or even know if it's possible to implement this idea on Less Wrong. I'm not even sure if it would be worth the effort)
There are posts that I upvote because I thought they were funny, mildly informative or well reasoned. Sometimes I upvote a simple (easy to produce) link to a good article. Sometimes I admit I upvote them simply because I agree with them (I generally don't upvote things I agree with if they use bad reasoning, but I am less likely to upvote something I DON'T agree with unless it is extremely well thought out, to the point that I actually updated my beliefs because of it.) I don't apologize for that - it's a natural outgrowth of the Karma system. It costs me nothing to give Karma to whatever I like and there is no means to enforce any particular usage of Karma.
But there are things I upvote because they were actually important and good and required hard work to put together. And I feel a little bit sad that the most I can reward those things is with a "click" that is exactly as valuable as the click I give people who said something mildly funny.
High value posts tend to acquire a lot of Karma because a lot of people feel motivated to click. But I think there is a qualitative difference between a guy who makes one amazing post that gathers 80 Karma and a guy who makes 80 posts that are kinda neat. I think it would interesting, fun, and potentially valuable to distinguish between those kinds of people.
So what if we had regular Karma, and then we had some kind of Superkarma. (Perhaps a good name would be "Status"). Status points would be genuinely rare - when you give one, you are not allowed to give another one for at least 24 hours. You can still give them to a funny joke or viewpoint that aligns with your tribe, but I think assigning them rarity would encourage people to reward genuinely important things. (I'm not sure 24 hours is the ideal waiting period, it just sounded nice).
I'm actually kinda amazed by how much I care about Karma. I get a "sweet, level up!" message in my head every time I see that I've passed another 100 points. But most of my Karma is from random comments. The two fastest upvoted posts I made were links to an article about the Singularity and a webcomic, neither of which required much effort on my part. The fact that my more serious posts are judged by the same metric is (slightly) demotivating.