Aside from learning as a way to acquire useful skills, there are certain things I learn in order to change the way I think. Echoing similar comments, programming seems to have altered my perspective as a kid and continues to do so. One example is learning Lisp. It's become popular to learn lisp not because it is practically useful in day-to-day coding (though it can be), but because it changes the way you think about how to program.

Similarly, studying abstract algebra might be a waste of my time (though I'll understand Lie groups and hence theoretical physics better), but the way it warps (in a good way) my mind cannot be attained by any other (present) means.

This might not be original, but my most valuable skill then seems to be learning how to learn, which includes honing my intuition of what is important to learn.