Apparently above $20M there is not much improvement in one's lifestyle. This is what I heard today in some office discussion. This much can give you a house big enough, a yacht nice enough, a car hot enough and new wife fast... something like that. And that above a certain money threshold there is nothing new to gain apart from more money and more power. And I thought "really".
Maybe they are two sides of the same coin though - if someone just likes money, they will keep on getting more. If someone spends more time thinking about others and helping, they won't get too rich any time soon. And there doesn't seem to be that much of overlap between those two extremes - of course there are cases of millionaires giving it all away to the poor, or being generally nice and helpful, but they are more like exceptions proving the rule.
Anyway, is someone has spare $20M and all he can think about is bigger house... There is so much to be improved in this world that $20B probably would not be enough, but even mere 20M could do significant difference - investing in specific organizations, funding projects around the world, helping.
I don't dream about money. It would be nice, however, to have more resources... To kickstart projects aimed to bring about moneyless economy preferably. The Venus Project / Star Trek style of managing society's needs.