The income from a service should ideally be proportional to how good it is. The income from a good should ideally be proportional to how good it is. The income from a work of art should ideally be proportional to how good it is. This would encourage people who want more money to provide better service, make better goods and create better art.
The way I see it though, a more popular artist would likely attract the attention of more people prepared to pay, so there would be some kind of relation to popularity. But people being prepared to pay when they don't have to might make for a more substantial measure of quality than just popularity alone.
I can also see art being made for the people who pay rather than marketed to children who would likely just take a free copy.