I would be glad to take the money of the people who say, "Money can't buy happiness." ;) :P
Having said that, I agree that after a point, more money definitely doesn't mean more happiness. I mean how much happier could Bill Gates be than Mark Zuckerberg?
yes, it has diminishing returns definitely
maybe Gates is a lot happier, but it will have very little to do with the fact that he has more money than Zucker