If I'm not wrong, I've seen somewhere (can't remember, where) that, an upvote on comment raises the reputation with +2. If it's never implemented, that can be implemented, because:
- There are many comments, that satisfy the question-asker as an accepted answer for his/her question.
- A comment upvote doesn't mean a Facebook "like" button.
Therefore, an upvote to good comment can raise the reputation with +2.