Yes, for some to many. Crossovers, caps, parts, Drivers, materials, cone materials, surround materials, internal wiring, binding posts, and even cabinet designs have improved compared to 20yrs ago.
example:
VA: Helped a friend to upgrade his Vienna Acoustic Grand Mozarts. Replaced boards, caps, woofer surrounds, in the same cabinets on the first try. A marketed improvement just using better materials. 2nd try a better X-over design with modern measurement tools, software. Raised to another level again. It’s possible.
Hersey: Ask any Klipsch Hersey owner if their Version 1 speakers sound as good as versions 2,3, or the new Hersey 4s. Same basic speaker, better drivers, materials. Compare the old vs new versions and then ask if there is no change or improvement.
Quad57s: Dave at Marihart Audio completely redid his Quad57s, every single bit replacing what he could or simply using updates parts with the same basic speaker design and reports are in, he’s absolutely thrilled with the results. Super cool upgrade!
Mine: AMTs, better crossover parts and drivers with Nomex cones with better materials, new material diaphragms, decent solder, connectors, binding posts sound notably better than 20yrs ago.
I worked on a speaker assembly line early 1980s, and most of the internals were marginal compared to what we are in decent quality speakers today.
Yes, sure, in many cases with new speakers or upgrade kits too for old speakers as another option.