What I have found is that the majority of "happiness from money" comes from the financial security, not actually spending the money. The reduction in stress going from a chronically broke PhD student to having 5 years of living expenses in savings is huge.

It's the knowledge that you can immediately solve almost every problem that pops up with a bit of money, and figure out the details later. Missed your flight? Book another one. Car trouble? Call assistance and take an uber. Lost your job? Take a short vacation and then hit up your network on LinkedIn.

And in most countries in Europe, you can feel secure with a lot less in income/savings than in the US. You don't need to worry about what your health insurance does not cover, probably don't have any student loan debt - and probably don't need to worry about a college fund for kids, can commute by public transport in cities, have better unemployment protections, and so on.