Yes. It would be a good way to fix misclicks. However, I would recommend a quick time-delayed lockout similar to that present for comment editing (or is that lockout related to child comments? It's never been clear to me). That would reduce dog-piling effects and would keep votes permanent from a semantic perspective.
My thoughts exactly. It's not hard incorporate one, not sure why this doesn't exist yet.
Better UI/UX around up/down voting would be a better solution
Definitely!
Seriously, someone down voted this?
It was a mistake
No. Karma doesn't really matter, so it's not important if you misclick.
If karma doesn't matter, then that is an argument for not having up votes for comments either.
It's not like there aren't other reasons.
unvote would be nice due to misclicks, or fix misunderstandings when initially reading a comment (e.g. in cases delayed detection of sarcasm.)