That's cool! I do all of those things as well, minus the uni classes and open-source. But for someone who has no interest in travel, then learning foreign languages would be a waste of time. I personally consider writing open-source software a waste of my time because it would be taking away from my closed-source side project ventures.

You can totally min/max your entire life and only do things for self-improvement, but then to what end? What do you expect to derive out of the continuing education classes that is going to be significantly valuable to your life/career?

I think it's important to note that many people are actually quite satisfied with their position in life, a lot of us are making a lot of money engaging in interesting work, so at a certain point doing things for the sake of minimizing opportunity cost comes with diminishing returns as you've already made the most of the opportunities you've already had. The whole point of working hard is to reach some stage of life where you can actually reap the rewards and have the time and resources to enjoy yourself however you please without worrying about it.