1. This is trivially disproved by observing people who have accumulated a lot of wealth. They spend it on dumb shit all the time.
2. Buying a Tahoe is not "spending much" if you are a billionaire.
3. Most wealthy people do not become wealthy by sticking to formulas in garbage self-help books: they inherit it, they become famous entertainers, they become successful professional athletes, they're former politicians who make insane amounts of money on speaking fees, books, and sweetheart access-based jobs. They're people who've created singular inventions or companies that produce dramatic payoffs. Sure, Warren Buffet (a wealthy, connected child who was able to access enough money to bother investing with thanks to birth advantages) had not plowed all of his earnings back into the fund, he'd be poor now. Good thing he drives shitty pickups. Bill Gates drove a Porsche when he was in his 20s. Larry Ellison owns most of the beach in Malibu and the biggest, tackiest, dumbest yacht the seas have ever had to bear. The Koch brothers are heirs. The Waltons are heirs. Michael Bloomberg has two jets and a double double townhouse in the most expensive part of Manhattan. Walton, Walton. Zuckerberg bought all the houses around his for extra privacy. Sheldon Adelson built a 50k square foot house in the wastes of Nevada. Larry Page and Sergey Brin built a fuck plane full of california king-equipped suites. I'm just going down the wikipedia list of wealthiest americans in order.
Good luck becoming a billionaire by skipping out on the guac at chipotle though boss.