Researchers at Princeton University have found that the positive effect of increasing income on emotional well-being, in terms of greater happiness and reduced stress, tends to flatten out at higher levels of around $75,000 per year.
People with rising incomes want more expensive consumer goods and services as they grow older, which tempers the positive influence of income gains on happiness. The positive improvements on happiness are also short-lived.
Americans are happiest when income and wealth are distributed evenly across members of society.
TL;DR: Live in an egalitarian society and aim for $75,000/year salary. Anything above that would make you adjust your consumer taste accordingly, which would not bring any lasting improvements on happiness.