IMHO the sole purpose of wealth is for insulation and self preservation.
The question is - how much money do you really need and how much are you going to be able to earn?
For most purposes, if you are willing to forgo the conspicuous consumption trap, at about 2.5 mil you and your family become insulated from the need to work to survive. This is due to this calculation: 2.5mil x 5% interest earning p.a. = $125,000 x .7(taxes) = $87500 which should keep you going ($7300 monthly =$3000 mortgage, $750 cars, $750 insurances, $750 fixed utilities with $2000 disposable income although more than likely you have paid off the house and have $5000 monthly disposable income.)
At $10 mil you ensure a very high income for yourself and assure your children and their children's future. You can contribute to politics prominently and insulate yourself significantly from life's vicissitudes unless you are dirty.
Somewhere between $25-$30 mil, you start to have more cash than you can realistically spend - about a mil a year in interest for doing nothing but sitting on your tush without touching the principal. After the fifth house in an exotic locale, furnished with Versace - what's the point?
At $50mil plus, there's a major choice you have to make. What are you going to do with the $$ you can't spend? Do you give it away, or do you want to create a business.
IMHO, not that it really is taught in our society any more (used to be in the british paradigm), that degree of wealth creates a heavy social responsibility. At that time, you have an opportunity to create a business that creates jobs and opportunities for others. "When a person has a job, they've got a chance." Why has that point been lost on our current crop of CEO's?
One of the happiest times in my life was one of the most difficult financially - I was clearly struggling and probably effectively at the poverty line. But I had fantastic friends, a great girl, and the time to enjoy them. In fact, all I particularly want to do with my life is to get back to that kind of situation, but with my future and my children's future assured. The rest of my happiness will depend on myself, not my bank account.