Hey,
I'm not sure whether this has been suggested before.
I find "thanks" or "like" button will be useful because:
1. It shows appreciation and encourages people to help. Of course the help itself feels good but everyone would feel happier knowing their help is appreciated.
2. A majority of helpful posts are not qualified for a rep
3. Posting a new reply just for thanking is more abusive and spamming to the forum than simply clicking "thanks button".
Let me know what you guys think.