I don't know if this will be helpful, but one thing I've been thinking about is that the reward system can be thought of as an exchange: the blockchain is giving a person a certain number of Steem and SBDs in exchange for the post being made public on the chain. The "prices" of these exchanges aren't taken into account by the price-tracking tools the way that a Steem-for-BTC trade on a public exchange would be, but people can informally do it. If they go to the trending page and see a low quality post there, and they see that lots and lots of Steem and SBDs are given to that post they develop the intuition that the value of a Steem is 1/Nth of the "true value" of a low quality post. I am under the impression that the bulk of rewards flow to a relative minority of posts, so it might be the case that you can maximize the efficiency of quality analysis by incorporating the volume of rewards covered by the analyzed posts into a metric.