These money-can't-buy-happiness theorists should perform an experiment. Find two people of equal wealth; take all the money off one; give it to the other. Then ask who is happier.But maybe it's too quick. It could be said in response to Tim that, of course, there's some lower income threshold below which happiness will evaporate for nearly anyone falling through it. But above that threshold, so the argument would go, income has little influence on happiness.
So here's a modification: find two people of equivalent wealth, take all the money one of them has above that minimum threshold, and give it to the other. Then ask etc.
Anyway, maybe it's not happiness people are interested in, but something a bit more complex, the access money gives them to resources and opportunities. Hey, maybe it's just money.