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Materials (items/goods/machines), like brain, are yet another form in which knowledge is stored. Knowledge, conversely, is created like and as material. They are in fact one and the same. However, some forms of knowledge are conceived to be unstored, ethereal entities.

Depends why you're buying, I guess!

Also, I think selling "art" is in opposition to the purpose of art. Ideally, artists do their work for free, and give it away to whomever they feel wants it most. This is true for all work, not just art. And it's why we need to separate access to basic needs from work.

Depends if you are doing it because: you appreciate art Or You want to be appreciated for buying a lot of art

This reminds me of Alan Watts and his discussion of what materialism really is. He makes a compelling argument that the superficial West is not materialistic. We do not honor materials and treat them with reverence because our culture is based on consumption and disposal. Art too

Art is a material that represents an idea.

Both

Depends on the “art”