To me, a valued blog post should be one that causes the reader to take some kind of action, to provide influence. The action might be to get them to come back and read more, or it might be to go some other place and take part in an exercise of some kind, but regardless, the post should engage the reader to be a really good post.
With that said, I obviously have quite a few blog posts that will be getting re-worked because they don't necessarily meet my objective of getting you to take action, regardless of the fact that they are evidence of me taking action!
Now before you get all excited and think that I don't have the right idea, remember that this is my goal for the posts on this blog. If you have a different idea, I welcome you to share your viewpoint and influence how I see what a blog post should be.
This idea continues to the goal of comments I post on other sites. Every comment made should be intended to capture your interest in what I'm saying and then drive you to learn more about me. I want you to click either on my profile, or on my link and end up here.
When I first started posting comments, I would often praise the person that made the blog post, but constantly praising someone without question or expression of my own ideas leaves me without achieving a goal of capturing your attention.
Commenters that constantly praise the blogger are essentially eliminating any value that they bring to the table, as they are unable to offer a unique perspective to the conversation. If you're truly a follower and are inspired from the post, ask a question so you can dig deeper and learn more.
If on the other hand, you have a different view point, a question can lead to more definition and actually show you as having equal or superior knowledge causing other readers to seek out your knowledge and spend time at your blog.
This can also be done through an expression or example of how you apply the point the blogger is making.
Consider praising a blogger as you would wait for the Don't Walk sign to go out at a street corner, and asking a question, or expressing a different view as walking when the Don't Walk sign is illuminated. Just make sure there are no cars coming, another words, don't let your words collide with your intended reader of your comment.