Here is an interesting article by Elif Batuman on the value of literary criticism. She has some interesting things to say about Freud, then discusses Marxist criticism, but then ends by talking about the "neuronovel." She argues that one of the roles of good criticism is to move the art forward. However, she ends with the entirely correct observation that it was in the creation of a new work of art -- Don Quixote -- that literature took an evolutionary turn away from chivalric romances toward the modern European novel. It seems unlikely that Cervantes was reading the latest criticism of the chivalric romances and then came up with Don Quixote, yet one also cannot just toss aside the fact that there is a great deal of criticism which those of us who write plays, poems, and/or fiction read (and often write).
Perhaps the key is that authors need to be influenced by the latest ideas without making their works "about" those things. Certainly knowledge of this or that psychological disorder can help create a certain level of verisimilitude for a certain character -- even the main character -- but if the novel ends up being "about" that disorder rather than about the characters and the plot, then the work fails as a work of art.
Perhaps Elif Batuman is right, though, and it's time for a new Cervantes. We must remember, though, that Cervantes celebrated as much as he criticized the chivalric romances. He had to know them well to make fun of them as he did -- and he had to love them to have known them so well.