I did drive my '55 1st GMC daily for a while. I tend to change primary daily drivers about once a year, usually because I got something 'new' and want to drive it instead of the 'old' one.
Living in Boise I'd say there are days, maybe weeks, in July and August when air conditioning are almost a requirement. But when I lived near there I spent one year driving truck out of field with no air, and I survived. Probably didn't smell good, but I survived.
My current daily driver is a 23 year old car (with air), my primary alternate is a 17 year old pickup (with air). My '55 1st GMC (no air) is licensed and insured and can pretty much take over any day I choose.
For me one of the keys to having an old daily driver is having an easy alternative for those days when you can't handle marginal defrost, no power steering, no air conditioning, rattles and harsh ride, or maybe the old truck is simply broken. Being able to jump in something else makes almost anything acceptable as a daily. So far this week I've driven all three for various reasons.
As for the cost, I don't drive a lot, probably less than 20,000 miles a year even when I take significant road trips. My alternates rarely run more than a few thousand miles a year, and my primary no more than 10,000. I don't owe money on any of them, pay little insurance, and shop for deals on parts.
If you have enough money to run a cash operation lots of old ones is not an expensive way to go. Month to month payments on something new is probably more cash flow friendly, but impact on net worth is higher.
