I assume that Kaj, with over 30k karma, would care even less about maximizing karma.

I certainly can't speak for Kaj, but I'd hesitate to assume that people with a lot of karma care less about getting more of it. After all, caring a lot about karma is likely to increase someone's chances of getting a lot of karma in the first place.

However, I often make commenting or posting decisions which I expect to be karma-suboptimal, and so do many others here.

As do I- I try to keep my upvote percentage on recent comments high, and so sometimes will avoid controversial subjects (unless it's one of the controversial subjects that I have decided to always discuss, in which case I still try to comport myself in a way that minimizes downvotes), even though a +3-2 comment would result in an additional point of total karma.

But the primary impact karma-maximization has on me is it urgifies generating valuable content for LessWrong. I finished my Decision Analysis sequence as quickly as I did because doing so put me at the top of the Top Contributors, 30 Days list (which was only 5 people back in 2011), and if I had delayed the first post would have slipped to more than 30 days ago, and I wouldn't have had enough to leap over lukeprog. I kept notes and wrote book reviews when before I would have just read books. And so on.