If one is going to be consuming entertainment media anyway for psychological reasons (e.g. it makes you happy) it would be useful to maximise the side benefits one gets from that media to save time that one would use to get them in other circumstances. (E.g. reading fiction with strong political philosophical themes as a supplement/alternative to reading introductory texts on the subjects).

Also, if nothing else, people enjoy discussing and analysing media, if people do enjoyable things in the less wrong community they are more likely to spend time there, hence contributing to human rationality.

It's probably more an effort to practice rationality than refine it. Finding good media to entertain, and possibly bring new ideas is (at least) fun. And it's better to take the word of people who already know the quality of something than to spend too much effort or wasting time on things you end up not enjoying.