The Mona Lisa isn't important except that you can sell it for millions so you can use that money to get the important things. Why is a painting important? Why is art important? Self expression is cathartic for the expressionist, however for the viewer, it gets mixed reviews because people assign whatever value their disposition allows them to assign. That doesn't make art important, it makes catharsis important.
Do you know what the word "important" means?
Why is a book important? If you can get a million for it, then it's important if you need the money. That makes the money important, not the book. If the book was important, you wouldn't sell it for money.