I worry that blanking your mind is a tad underspecified. If you delete all your current justifications and metajustifications, you become a rock, not a perfect ghost of decision-theoretic emptiness. What we want is to delete just our current notion of a good means, while preserving our ultimate ends, but the human brain just might not be typed that strongly. When asking what is truly valuable, it could sometimes seem that the answer really is "whatever you want it to be"--except that we don't want it to be whatever we want it to be; we want an answer (even knowing that that answer has to be a fact about ourselves, rather than about some universal essence of goodness). Ack!