How practical is a strict car wash regimen? Here, I'd daily drive to work, and if the roads were salted, it sat coated in that all day while parked at work. When I drove back home, I suppose I could stop at a car wash, or when I get home, spray the undercarriage but it's not always practical, particularly if it's below freezing and that results in an iced driveway. I could put ice melt on the driveway but then even my driveway subjects it to salt deterioration.
My best guess is the friend had road crews using something like beet juice instead of a salt to melt the roads, that it was not driven for 20 years worth of winters on salted roads without something more going on, even if that something was only a good factory undercoating.
However, define "rust bucket frame". I have a (previously used as a) daily driver older than 20 years that still has a safe frame, but it's not like there isn't a lot of rust to be found. Floor pan developed a big hole, brake lines needed replaced, rocker panels and dog legs got replaced and now need it again. Lower rear shock bolts shear off every time I attempt to remove them, sway bar link bolts rust through, and to some extent I just have to accept it if not willing to put it on a lift and undercoat every year or two because there's no way in your driveway without a lift, to practically coat (or wash) every nook and cranny. However what you can do, is coat things in silicone grease when you replace them. They'll get ugly grimy looking but take a lot longer to rust out. I mean fasteners in particular, then there's using NiCu line for brakes.
Ultimately, I just want the rust to not be the reason to send a vehicle to the graveyard before some other failure like engine or tranny happens, where repair exceeds the value of the vehicle. At the same time, any vehicle reaches the point where it seems like every few months, it's nickel and dimeing you and you just want to drive something that doesn't need that much attention, and rattles/squeaks less. I'd keep a 20 y/o 4R for the utility of hauling/towing, or use on salted winter roads to save a daily driver from it, but agree with your friend to get something newer to daily drive otherwise.
Lastly there is value of time and cost to maintain as a perspective. Suppose value of time and cost to maintain ends up as $150 a year. After 20 years, that's $3000. If the vehicle is no longer worth much more than $3K, it doesn't seem worthwhile. Here's a case where covid related shortages and escalating new vehicle prices due to tech are a wildcard, but in the past that rationale made sense, that it's not wise to spend more to keep a vehicle than it's insurable value is worth, or you just end up going to great lengths trying to, then some texting teenage driver runs into you and totals it anyway.
Just sayin'... life is short, how much work to put into a vehicle worth little once it is 20 years old? Makes sense if you look at it from the green perspective of not polluting by buying a new vehicle, or makes sense if you DIY all the work to squeak by with far lower repair expenses, but that is a highly subjective decision, and can change as you get older. The older you get, the less you want to be babysitting *anything*.
Back to the point, do I want to spray the undercarriage of my vehicle every time I drive in freezing weather, winter slush? Heck no.