Nice analysis @crokkon!

I've thought for a while that there is a weakness in the steem rewards system that is open to abuse. While @steemcleaners can flag any spam accounts creating post rewards, they can't reverse curation rewards without destroying the rewards of the original poster (who could be anyone and entirely unrelated to the bot network). Of course the rewards are small, but get enough accounts and it soon builds up. My guess is that is where the SP is coming from, although like you say, more analysis would be useful.