I’ve earned greater than ~$100 for my comments a few times, such as this recent one on my own blog post, which was greater than the reward for the blog post at the time of writing this. I think I once was rewarded $500+ for a comment.

A comment can provide some unique point that some whale or dolphin might find important enough to upvote with 100% SP; whereas, they might not agree so emphatically with your entire blog. But still it is good to write blogs as well to increase your reach and following. Social networking is all about building relationships and a reputation. Social networking marketing could also include other strategies such as gamification (subset of psychological matching and manipulation).