In your title it says commenting, but the thread itself you are talking about comment voting. Those are two completely different things.
Anyhow, it is not worth it, as you need to at least log in into 15 accounts and vote up a comment. If you have the time, go for it, but if you want do it efficiently, I would look into getting a comment rater coded by a freelance company or something. At the worst, I would hire somebody to do this for me (manually).
Anyone still doing youtube? - Yeah, lots of us are still doing YouTube, but commenting is more for the people with the tools. Comment spamming can be done by anyone, but comment is more "quality > quantity". I did a test: I commented on two very similar videos with similar traffic. I did 1 comment with 26 thumbs up, I got 3120 clicks in 1 hour, and the other video I spammed and got 76 clicks. I can easily say what is best now.