Indeed if someone has a comment worth recognizing, upvote for sure. I'd give my 5cents to a great comment any day lol. I also believe that simply responding or even commenting on "unfollowed" new content are both great ways to retain or accumulate new followers. When someone engages with me in a post, we both benefit. Not only do you get to know another user (be it only a little), you are ten times more likely to go check out their blog.