Interesting. There seem to be two separate issues here: karma as motivation, and karma as metric of effectiveness.
Re: karma as motivation. Since you've been here from the OB days and have been sufficiently motivated to participate for the past several years, I suggest that the problem isn't your absolute karma or the rate of increase of karma, but habituation of your dopaminergic motivation system to the amount of karma you get per comment. I suggest (partly from theory and partly from personal experience) that if you go away from LW for a few months (or maybe just a few weeks), the habituation will reverse itself, and you'll be sufficiently motivated to participate again.
Re: karma as metric of effectiveness. This seems a much more difficult problem. Karma is a dimensionless quantity. We know that the sign of your total karma is positive, which suggests that you're doing more good than harm on LW, but how can we convert a karma value into an estimate of how much good you're doing, and compare that to how much good you might do elsewhere? You seem to have some intuition about that, but I'm not sure what it's based on. (Could it just be the affect heuristic? I.e., your habituated dopaminergic system makes you feel bored about participating on LW, and you translate that into a low estimate of effectiveness?) This might be a good question for a discussion post, unless there's an obvious solution that I'm missing...
Recently, I've collapsed (ascended?) down/up a meta-learning death spiral -- doing a lot less of reading actual informative content, than figuring out how to manage and acquire such content (as well as completely ignoring the antidote). In other words, I've been taking notes on taking notes. And now, I'm looking for your notes on notes for notes.
What kind of scientific knowledge, techniques, and resources do we have right now in the way of information management? How would one efficiently extract useful information possible out of a single pass of the source? The second pass?
The answers may depend on the media, and the media might not be readily apparent. Example: Edward Boyden, Assistant Professor at the MIT Media Lab, recommends recording in a notebook every conversation you ever have with other people. And how do you prepare yourself for the serendipity of a walk downtown? I know I'm more likely to regret not having a notebook on hand than spending the time to bring one along.
I'll conglomerate what I remember seeing on the N-Back Mailing List and in general: I sincerely apologize for my lack of citation.
Notes
(I've also heard a handful of individuals claim that SRS has helped them "internalize" certain behaviors, or maybe patterns of thought, like Non-Violent Comunication or Bayes Theorem... any takers on this?)