I think it is really important that we upvote (genuine) comments on our posts as comments 'add' to the overall value of the post and therefore should be rewarded in my view.

It also shows that we've read it and acknowledged their input (which, after all, is equivalent to a post itself in the eyes of the steemit platform).

I get it, that for dolphins and whales, there may at times be a heck of a lot of comments to wade through but the effort to respond with at least a token upvote is appreciated.

One thing I want to try to do more is to upvote other's comments in the comment section ie on other people's posts.