Agreed. Though I can only speak anecdotally, every wealthy person I know - which I'm defining here as would not need to earn any more money between now and the day they die and still live comfortably in their chosen lifestyle - is not a spendthrift.
One of the wealthiest men in the world balked at an aircraft avionics upgrade that cost less than his income for one day.
And more often than not, even seemingly-frivolous expenditures have ulterior money-making options that may have long-term returns. Richard Branson may seem a spendthrift, but I assure you that nearly everything he does has long-term gains in mind. (He is not the person referenced above, btb.) Some pan out, some do not. But an expenditure that is knowingly not a good buy is a rare event.
I don't know if the research is still the most current, but in the Millionaire Next Door study, the ONLY absolutely consistent factor for American millionaires was their marriage to frugal wives.
Frugality is very heavily correlated to wealth gain and retention; to the point where I'm comfortable calling it a factor in causation.