Sound quality of Newer versus Older speakers

Newer, by far. Cone materials are far superior, even more so at the lower end of the spectrum. Ditto techniques for reducing varying inductance effects. Better capacitors. Far less cabinet resonances. More consistent dispersion.

all you say is true...however, if behind all that tech you don't put a engineer with an exceptionally good hearing and musical culture, the result is a round Zero. This is what happens to many companies...they focus on tech specs, even the wrong ones probably, aggressive marketing and fancy design. For those companies sound quality seems the last priority. In my very limited audiophile experience i know that dynaudio is one of them. They changed their priorities in 2016. In fact there are almost no happy contour 60 owners around. It's full of dynaudio fans which praised the old product lines and which agree the new product lines are a disaster. Despite better materials, better capacitors, better cabinet design (sure??? My contour 60 sounds like a wooden box emitting sound inside out). If you have a 10K budget for a speaker you can get crazy stuff in the used market.
 

It's like with everything else, like a super modern kitchen with a crappy cook, a F1 car with a crappy driver, 100mpx camera with a stupid photographer and so on. Technology has to be driven...it doesn't drives itself. Big companies are often driven by financial targets and less y passion and commitment.

Are there differences due speakers being voiced to the music of their era?
I remember hearing Dylan's "Desire" on some 70 era's monitors with big, sloppy woofers, and thinking, "Wow, this is really right."
Sort of like movies' voicing of natural speech changing over time: surely nobody actually talked like that in the 70s? :)

Newer, by far. Cone materials are far superior, even more so at the lower end of the spectrum. Ditto techniques for reducing varying inductance effects. Better capacitors. Far less cabinet resonances. More consistent dispersion.

Most of "new materials" are cost reduction and marketing.

Best cones are paper cones.
Best magnets are field coil follow by alnico.

Especially it is true for people who listen classical and jazz music.
Even rock music and  sounds much better on 15 inch paper cone speakers like 70x JBL.
If you listen modern POP music that was mastered for boombox, why do you need Hi-End system at all?

Older audiophiles like the comfort of their old colored music. It works for them. It does not work for everybody. 

Most of "new materials" are cost reduction and marketing.

Best cones are paper cones.
Best magnets are field coil follow by alnico.

At what price point? That is not true at all at the high end. Not even close. Alnico is a magnet material type. There is far more to a motor than the magnet type.