You do you, I'm just saying that it doesn't often make financial sense. If you buy a $300k old (we are talking OLD) and spend $200k in retrofitting, you don't necessarily have a $500k home (although you might), you very well could have a $400k home. Yes, you can do a lot of the stuff yourself, if you have the skills, but the truth is; not many people are framers/trim carpenters/drywall hangers/drywall finishers/plumbers/electricians/AC guys/insulators/masons/concrete guys. If you are a journeyman skill level in 2 or 3 of those, that's fantastic, few people are in more than 1 or 2; let alone 5 or 6 trades.
Also, I do agree that in many cases, you can get 80% towards a modern home, with 20% of the effort; but to get to that equal level, it's a lot of expense. Not all old homes are worth retrofitting. My mom's house is a 1949, but was very high end/forward thinking for 1949; with large rooms, many large closets, and 3 bathrooms. Many old homes aren't. Even still, to install central AC would be enormously expensive, not just for the HVAC, but the need to add dropped cielings to fit duct work, wall repairs, ect. The walls are all wire lathe and plaster. After decades of window units, she did have several mini splits installed; but you still have annoying old home problems/design issues; like ungrounded outlets, only 1 outlet or maybe 2 per room, plumbing fixtures that parts are no longer made for, something like a R-5 in the cieling; maybe R-3.5 in walls; and non-standard window/door openings.
Many of the old farm houses have like 24" doors, Itty bitty rooms, 1 bathroom, 100 amp electric services, ect. I'm not beating them up, you just have to know what you're up against; and make a decision that is smart for You. Frankly the 1950s/60s homes are generally better than the 1970s; and all of them, even brand new construction have issues.