In my opinion, what's missing in these aggressive "we don't need a thank you / like / whatever bullshit" comments is acknowledging that in some cultures, it's polite to thank for help, and when asking a question and somebody takes some time to write down a nice answer, some people feel obliged to say thank you.
I think being thankful is not such a terrible thing that it deserve such harsh criticism.
And I like the idea to offer a separate button for this, as it would collect this kind of "noise" and put it somewhere else.
Could be a counter somewhere where people can see how many people have thanked them, but who doesn't bother won't be disturbed by this, and especially not receive notifications about "thank you" comments.
Yeah, I know they shouldn't be made, but welcome to reality, people make them anyways and always will. Because humans are diverse, and maybe it would be nice to open up for diversity a bit and not only support what white angry men think is appropriate interaction (sorry for the rant).
In the end, everyone would profit: The comments stay clean from personal stuff like "thank you", "+1" or "that helped me too!!!", users can express gratitude if they want to, the ones that don't care about it will be bothered less by notifications - to me, it's a win-win-win situation.
You could even display a hint for unexperienced users that press "thank you" without upvoting (or accepting the answer) first, where you ask them if they don't want to "upvote and thank" at the same time...
I wouldn't be surprised if that also results in more upvotes, because I can imagine not everyone is aware what upvotes are for.