On your second question: I believe that the amount of influence that a vote has decreases after you've voted more than 40 times a day (at least that was the case several months ago according to several high profile Steemit members. And though there is nothing to stop thousands of members joining a non-quality based upvoting group who upvote in exchange for upvotes, the fact remains that the value of your upvotes is a measure of your steem power, which is earned through the value you put forth on the site. As to why a hundred or a thousand people who already have established blogs that provide real value (and which receive profit in return) would need or want to be part of a group I don't know.

I was however lucky enough to be part of a channel on Rocket.chat in which members posted and upvoted each others work in a quality based setting (which was definitely a boost given that it was quality based, and we were therefore engaged in a secondary form of curation, I believe.) - I hope this clarifies your second question @sinzzer - and if anyone happens to know that it isn't 40 upvotes a day before voting power diminishes please correct me!