Based on life experience and things I've read, I've found that once one reaches a level where basic needs are met and there's no need to worry about where the next (or the next three dozen) meal(s) come(s) from, money does very little to make people happy. Hell, as a student right now, my net worth is very, very negative, but I'm also very happy because every day I get to do exactly what I want to be doing, and my immediate future is pretty secure.
Money is really just a form of freedom. If people are free to do what they want, they will be happy; if not, they will be miserable.