I think GP doesn't mean "returns" as in investment returns. I think they're talking about like... living. The utility of buying a second (or tenth) house/car/whatever is drastically lower return than the utility of buying your first one.
However, the utility of money starts to drastically increase once you reach a tipping point where it can start allowing you to wield real political power.
The graph of monetary utility may look like a logarithmic graph at first glance, but that's just because it's more like a C1 + (x-C2)^3 graph where you haven't followed x far enough to the right.
Remember when Michael Bloomberg spent 500 million dollars to be on the Democratic debate, and Elizabeth Warren burned that money down with a single zinger?
