Let me preface this by saying that I always seem to regret being nice. It's the people that are mostly unaware of others that seem to be the most happy. These same people don't seem to have a problem being cruel as the feeling comes to them.
This doesn't sound good, but it's true. This doesn't have much to do with this story though.
A couple years ago I was on the bus and this kind of thing was on my mind. Over the years my best friend and I have switched between who was more dominant and a couple years ago it was him. He wasn't nice about this either. On the bus there was a woman and what I assume to be her two daughters. The daughters were kind of playing around the bus and climbing on things. One daughter was obviously more dominant; she was the one basically deciding what game they were playing and she didn't let the other forget that it was 'her game'. After the dominant one was particularly rude, the other went off and did her own thing and start playing behind a seat or something. She seemed to be pretty amused with what she was doing.
After a while the dominant one got bored and went to see what her sister was doing. After seeing that she was having fun, the dominant one joined in and her sister accepted in an obvious way, because she was still busy amusing herself. After that they seemed to have an equal understanding with eachother.
I don't know about nice people having more fun, but the moral if the story is if you have more fun people will be nicer to you.