When you have a low level of interestingness, the marginal utility gained from improving your interestingness will be quite significant. If you have a high level, then you probably don't have to bother too much, but there may still be some actions with minimal cost that might significantly improve your interestingness. For example, if you have never seen a science fiction film before, but you know many people who are interested in science fiction, then you can take half a day, watch a few films and then have something to talk about these people with.