Sorry to sound rude, but I can't see any point to this at all...
Like a few posters have said, if someone posts something deeply emotive, or very helpful and kind, and they get NO 'thanks,' it's going to make them feel quite low and pissed off. Like nobody cared about what they said, and no-one is interested.
The edit button is brilliant, and I am really happy that MN have now given people the ability to edit. Only thing I do wish, is that there was not an 'edit history...' I hate that. I think that if someone submits a post, and they edit it within say, 60 seconds (like, just correct a couple of typos,) that there's no need for an edit history.
You get an edit history on facebook posts, and for this reason, if I have made an error, I just copy what I have posted, and then delete it, and then re-post it/paste it ... with the corrections!
But yeah, a thanks button/gratitude button that only the poster can see seems pointless to me. Also though, I would not like to see a thanks button where all the 'thanks' are seen by everyone, as I have seen this on other boards, and it creates cliques. Eg, if 2 people are arguing about something (Lyn and Sam,) and Lyn gets 15-20 sets of 'thanks' and Sam only gets 2 or 3, it makes Lyn look more popular, and more 'correct,' and will make Sam feel like shit!
So, regarding the 'thanks' button/gratitude button ... it's a big fat NO from me.