Great post and analysis.

it makes me wonder what the purpose of the second payout is if the whales themselves seldom upvote after 24 hours

I had exactly the same question in mind. As there is no curation reward after first payout, there is no real incentive to upvote "older" posts.

The drawback is that the very good posts are forgotten as soon they pass the 24h milestone. This lead to over-production of new and new posts, with lower quality, which is quite the opposite of Steemit goal.