Child-like joyousness was what I was envisioning. The short story Paprika http://escapepod.org/2014/05/30/ep448-paprika/ ends with all humans long dead and the only remaining human creations are talking squirrels that, at least according to the story's brief description, live completely care free and joyous lives. That doesn't exactly seem feasible to me with living creatures having resource needs, but what if they lived in-silico rather than in meat? That would still have resource needs, but possibly far fewer.

I think I am unconvinced that the way humans... "work", for lack of a better term, is the optimal one. As you said, people who are at the high end of the spectrum of intelligence don't seem to be happy quite as often (not to suggest that I think people should be dumber, but being both intelligent and ecstatically happy most of the time without the use of life-shortening drugs would be nice). I was curious about what has been discussed on the subject already, but I guess I chose the wrong way to ask it.