Commend, if accepted by mods, should result in a visual difference in the display of the post somehow opposite of how flags works: pin to top, really small star or something. Maybe a list of exceptionally good answers in the users the profile.
I was once "caught" for doing something correctly that all teenagers tend to fail on (technical, trivial thing) and ten years later since then I realized I had always got it right after that day when someone told me that they appreciated it.
I don't know if this is a good idea, but I wanted to mention it.