A lot of the theoretical frugality is also a roundabout way of showing off. In certain areas, such as New England, it's not enough to have money, it's how old your money is. So if you have a house on Nantucket, and you keep a 1984 Grand Wagoneer there, you're saying "not only do I have a house here, but I've had a house here for a long, long time, as demonstrated by this ancient car I bought to keep here decades ago." Or it's "I've had money so long I'm no longer interested in showing it off, so I continue to drive this Mercedes 560SEL I bought new back in 1989." Amusingly, an entire cottage industry has popped up selling restored Grand Wagoneers and Land Rover Defenders (sold new here 1994-1997) so that people can, for mind-boggling sums of money, purchase the appearance of old money. It is honestly a fascinating dynamic.
Source: I grew up in and around the old money parts of CT (without having any real significant money, old or otherwise)