Some of the research on happiness has shown that though more money above a certain level does not correlate much with more happiness, having more money than your neighbor does.
And having less money than your neighbor is correlated with lower happiness.
Most recently there is a study in the news by sociologists Glenn Firebaugh and Laura Tach, called “Relative Income and Happiness: Are Americans on a Hedonic Treadmill?”
They found that physical health was the most important factor in the happiness of their subjects, but their relative income was second most important.