Diminishing marginal returns... as in your example of reaching satisfaction at $75K a year (I think it's $83K now... inflation).
In the US, we measure too many things in terms of money and wealth. And it becomes a catch-22... a bit like @pastbastard commented, a cycle. I do far more than the bare minimum... at things I don't get paid for, but mostly I cant afford to because I have to put my energies into income producing things... that I don't care as much about; so I get caught in "doing less."
And so, I have to sit back and consider your question in the context of the reality that I am perhaps a "barely minimum" human DOING, but a much above barely minimum human BEING. Kindness, compassion, helpfulness, honesty, dedication... their value is harder to measure.