>How do you justify the importance of literature? Of philosophy?
You should start with how you justify anything. Is anything sacred? Is your culture sacred? Is your language? Is a human important? Is it possible to justify logic without omniscience, or a knowledge alien to humanity?
>to learn
Next you ask what is the will towards knowledge. Obviously we have produced results that affect the world around us so we must say that our willing has opened at least a blurry eye to the universe. Thus we are striving still towards objectivity, that ineffable beyond.
>Could we not be going about this wrong?
What is most interesting is how we are going about this wrong and how changing the fundamentals of our will, our tool of access, can help us move further towards understanding the universe objectively, or as a "universe".
>For some people, it feels wonderful to read. Ideas feel important. The sensation is amazing. I'm a music fan, and we get a similar thing. Yet I don't care if other people feel the same way; what’s "important" varies from person to person. Why, then, do you feel it necessary that every person read literature or philosophy?
No and yes! Because not reading literature or philosophy is impossible for this species to do. The individual will can never be separated from that other will, the will to life, the will to power, the will towards the good, whatever it is that can't be named - that reading is not important to you is only a sign of your worth, your value to it. Unfortunately, you may be only the feedback that helps separate those who feed the beast from those who live in harmony with the beast. It would be better that everyone make literature and do philosophy than read one word. Telling stories about each other, for one another, and seeking the truth of matters for the love of seeking it alone.
The importance is that literature and philosophy are not just outside of you as such - there is no need for a return to tradition - but both are you, as much as you are by the means of some "power", political, environmental and biological. You are cultural, and to be a rational person that strives towards objectivity, just as the rational person asks why we ought to strive towards objectivity, you will refine that other will.
Again, it's not necessary to read, but there is no stopping humanity from striving to reach the infinite from their finite graspings.