[jondubois]

>> happiness goes up with increases in income at the lower end of the scale, but then it falls with higher incomes

Income and wealth are two completely unrelated concepts. Income doesn't mean much because you usually need to work harder to get more income; so the benefits are offset by the suffering of having to work harder.

Wealth, on the other hand doesn't require any suffering - It's just pure happiness. Wealth can buy you anything. The only downside is that it erodes your mental fortitude/willpower but if you have enough wealth, you don't need any willpower anyway because wealth makes all personality traits redundant - Everyone likes a rich person no matter what; to a rich person, personality is useless.