What is the justification for the nobility? Some appeal divine authority. In one world however, being of noble blood really does elevate you above the common rabble. By virtue of magical aptitude.
Another real world thing. White tea. Can only be picked two days a year, the two days before the flowers blossom. Could be a similiar plant that...is the deadliest poison known, cure known diseases or psychosis, or a potent herb that just tastes awesome.