Not sure if you're arguing for or against my point, but I'd say the purpose of feeling happy is to reinforce the behavior that got you where you are. Smiling (and the compulsion to smile, which few other animals have, though they do feel pleasure) is to signal your state of mind to your peers.

I wouldn't say (and wasn't saying) that the purpose of feeling sad is to cry or engender social signaling (parallel to happiness, the purpose of sadness is downregulation of behavior), but the compulsion to cry itself and the relief afterwards is about signaling.