Short Answer:
Yes, speaker technology has advanced. But, it would resemble something like a "smiley face" if you put it on a graph. The greatest gains would be at the low end and extreme high end of the spectrum.
Long(er) Answer:
Speakers commit errors of omission AND commission. They cover up, vail, compress, and remove things that were included in the original material (omission). They also create sounds that they shouldn't via resonances, microphonics, etc. (commission) The entry level has benefited the most from manufacturing efficiencies, upgraded material quality, as well as more attention to reducing resonance, early reflection, and vibration. "High end thinking" has migrated into lower price points and has produced surprisingly musical "budget-priced" speakers. On the extreme high end, the level of precision is off the charts compared to decades past, and prodigious attention to enclosure integrity has produced products that come closer to mimicking the sonic characteristics of a live performance than any time in audio history.
That being said, speakers in the target range of $3k-$10k (per pair) have been "getting it right" for quite some time. They used good parts and knew how, and where, to use them. Cabinets were robust. And they paid attention to magnitude of "little things", that when aggregated, produced something truly remarkable. But, modern speakers in this range are, indeed, incrementally better.
It is my view that unless you have form factor or esthetic requirements that can't be satisfied by earlier designs, you'll be happy owning a used speaker worthy of representing the performance in it's class -- and, keep the change.