you are right that this is a very decent way to earn money/SP.
I do have some things I'm really curious to know. So you have any idea how many comments you wrote? And how much time did it take?
My suggestion for users that try to earn via comments is to search for authors that regularly upvote comments below their own posts. And perhaps even more important follow and read stories you really like. Cause of you have fun, things are easy easier.