As someone who does "care"* about my ranking, I can confirm that it's all for the fun of seeing your number go up. The material rewards aren't much to write home about, since the unsolicited ARCs I receive are all electronic (not resale-able, not that I would) and most of them aren't things I'd necessarily pay money for anyway. It's just a fun hobby.
The Vine board, otoh, are -- as you say -- straight-jacket-wearing insane. I've sworn off that board because it was troll central. There are a LOT of good Viners, and the trolls comprise maybe 1% of the group, but almost 99% of the posts, and Amazon is utterly unwilling to do anything about it. I personally think there's a buildup of bad-will towards Amazon; I know that I was pretty frustrated with them as a company until I finally swore off the boards and got some distance.
*Admittedly not enough to delete-and-repost my reviews to improve my ranking. Not out of any moral reason, I've just been too busy to invest that much time into the ranking.
