The quality of production has gone up with CNC, but the quality of materials and the price people are willing to pay for things has gone down.
Also electronics have become more consistent and more efficient, but this actually meant that they became less musical. Now the best electronics for music are only produced half as well as they used to be in Russia and China. Tubes for example have stopped being produced in the US(as far as I know) and the Russian and Chinese ones aren't as good. NOS US tubes are still the best.
Tone capacitors are the other electronic component that has been killed by time. PIO capacitors aren't produced much at all anymore even though they're very simple(basically aluminum foil and tissue paper soaked in oil) though they sound better for audio applications.
Metal and wood for guitars has also decreased in quality because of worldwide demand. Most hardware now is brass, which doesn't resonate as well as steel or aluminum, which is what hardware was made out of in the 50s. Good wood is becoming more rare too because we've realized(hopefully) that we can't just go cutting down every tree we like, we have to keep forests well-maintained or there will be no more trees to cut down.
Guitars are now being designed to be very muddy too, to stay balanced with new solid-state electronics, and to give enough output to meet the excessive gain levels of today. Most modern pickups are overwound to ridiculous specs, 12-15kohms when 8k will do just fine.
Audio is a strange world where more efficient electronics = worse sounding because of the way we interpret sounds. There are certain harmonics our brain likes more than others, and solid state roughly reproduces all harmonics equally as well(not quite, but more so than tubes). Tubes accentuate certain harmonics that our brains really like, like a good tone wood. Solid state would be like building an acoustic guitar out of aluminum. Sure it produces the best sound from a mathematical standpoint, but it'd sound like **** to any sane human being.
Hopefully we'll progress to the point where we get something 'modern' that sounds better than the old vintage stuff. In another decade we'll probably all be playing molded hemp or organic plastic guitars with hex output into synthesizers/modelers with tube simulation anyways =P
One thing in audio that has really gotten better is audio reproduction though. CDs, Amplifiers, and speakers emulate very well what was originally played, so you don't lose even more harmonics to putting the audio through all those tubes and vinyl and alnico speakers again. I quite like CDs into solid-state stereo amplifiers and neodymium speakers, so maybe our tastes will evolve with the technology as well.
edit: Another testament to the idea that it's the technology and not the time that makes vintage stuff better is that new reproductions of vintage pickups sound just as good.
There is some nostalgia that goes into it too, though. Old stuff always seems cooler. There's also the organic feeling of old electronics compared to the sterile factory-produced connotation that new stuff carries.