You have described such a great concept in such a few words! The concept of diminishing returns applies to so many things in life, but yet so few seem to understand it.
In fact, I'd say in the case of money, it's sometimes the opposite. My mom came from the lower middle class, and now we live upper middle class and my mom says that while she does appreciate the money, it also becomes more complicated to handle it. Taxes become complicated. People become jealous. All kinds of things happen.