I have two relevant examples of modding old gear to make it better.
1) My beloved Marantz Model 7. It dulled the leading edge too much, I thought as a 19 year old. What to do? Saul Marantz very kindly sent me suggestions, notes on a copy of the circuit diagram, which I scrupulously followed. I put in a full-wave rectifier bridge in the power supply. I replaced the electrolytic capacitors in the phono section with solid tantalums (this was 1976…best capacitors I could get then). Replaced the paper coupling capacitors with Mylars (Cornell Dubliers, as that what was in the Audio Research SP3A). Replaced all resistors with metal film types. Finally, used GE 5751s in the phono section. Did it sound better? Hell yes…far more focus, tighter bass, huge sound stage. Nonetheless, 5 years later I replaced it with an SP6B, much better. My current Cary SLP05 with ultimate upgrade is vastly superior to both; it has better components and design.
2) I had my GAS Ampzilla, which I built in 1975, rebuilt changing out virtually all transistors (replaced 15 amp Motorola output transistors with 20 amp Toshibas), and replaced most of the capacitors with modern low-leakage types. It’s now pretty decent, much better than before. But in Mr. Bongiorno’s own words to me, new transistor designs available now, along with new capacitor types, allowed him to do things he could not dream of before. As good as my rebuilt Ampzilla is, my SST Son of Ampzilla II is substantially better…more refined…in all regards.
I totally get the car analogy, especially wrt weight. But the electronic controls of modern engines are pretty amazing, as is the improvements in chassis stiffness and suspension control and tires. A modern Corvette will kill a late sixties Corvette. Although I am not an electric car guy, they have phenomenal acceleration, even faster than Andy Granatelli’s gas turbine powered Corvette!