whoever wrote that book is selling you on a worldview. your quote is often repeated, but i don't find it to be true. i think it's wishful thinking for a lot of thrifty people, so they can feel superior by judging people they don't know by what they drive around in.
in my experience being a millionaire or not has absolutely no bearing on the kind of car you drive. some people like nice cars or sports cars, other people simply don't give a shit about cars, rich or not.
and from what i've seen, even the wealthy people who don't drive nice cars have other really nice shit, like $100k in road bicycles, or gigantic house(s) or a fully equipped fishing boat sitting in the marina. but they drive a prius, so they're thrifty and virtuous.
Rather than just anecdotes, the authors of the book did actual research and found that most people who have actual net worth above a million dollars did in fact get there by carefully managing their money, and conversely, most people who had the appearance of wealth in the form of expensive cars and boats, didn't have the actual net worth that it implied.
So, if you're judging someone's net worth by the things they happen to own, the whole point is that this is not a reliable indicator of how much wealth someone actually has.
my point is that you're doing the exact same thing, except in the other direction.
That, or a completely irresponsible attitude towards consumer debt. In most cases, the latter. So, this isn't really a very sound strategy for finding a mate who is financially sound.
Read The Millionaire Next Door. Most people who are actually wealthy drive moderate cars that are completely paid for. Since many of them own a small business that often works in a fairly blue collar industry, they're more likely to be wearing jeans and a work shirt rather than a suit.