It doesn't grant any new abilities as such, admittedly, but if you're interested in making the right decision, then rationality is quite useful; to the extent that choosing correctly can help you, then this is place to be.

Hm. My correction on that would be: To the extent that your native decisionmaking mechanisms are broken and can be fixed by reading blog posts on Less Wrong, then this is the place to be. In other words, how useful the study of rationality is depends on how important and easily beaten the bugs Less Wrong tries to fix in human brains are.

Many people are interested in techniques for becoming more successful and getting more out of life. Techniques range from reading The Secret to doing mindfulness meditation to reading Less Wrong. I don't see any a priori reason to believe that the ROI from reading Less Wrong is substantially higher than other methods. (Though, come to think of it, self-improvement guru Sebastian Marshall gives LW a rave review. So in practice LW might work pretty well, but I don't think that is the sort of thing you can derive from first principles, it's really something that you determine through empirical investigation.)