“Is there any data on whether atheists or more rational/intelligent people self-report lower levels of happiness?”
Apparently they don’t, judging by selected responses to the recent “Survey: What Do Atheists and Christians Believe (and How Strongly Do They Believe It)?” by Sam Harris. The relevant statement is probably: “All things considered, I am very happy with my life”, the fourth one under “Survey Results: Psychological Beliefs”.
I am not a moral realist, thus I imagine my behaviour wouldn’t change all that much.
My motivation to act one way or the other in any situation is based on a few things: my sense of rightness or wrongness, though other factors may override them (thirst, hunger, lust, etc), not on whether or not the act is “truly” right—I’m not sure what that would mean. I am skeptical of rightness being a property of certain acts in the world; I have not seen convincing evidence of their existence.
I nonetheless have this sense of right and wrong that I think about often, and revise according to other things I value (logical consistency being the most significant one, I think).