Buying used vs new speakers from a technology perspective

I think there's certainly some improvements in speaker design associated with electronics, material science and modeling/simulation tools that has resulted in improved performance.

When it comes to comparing 10-15 year old speakers to new speakers then there's certainly opportunities for time to degrade materials beyond regular wear and tear from usage.

I think there's certainly some improvements in speaker design associated with electronics, material science and modeling/simulation tools that has resulted in improved performance.

Plus one. 

A lot of folks like older drivers in fact very old drivers can be quite expensive on the 2ndhand market. Some materials have improved but some older materials Alnico magnets are one example are considered by many to be better. So no don't be afraid of older speaker the answer as always is better is better not necessarily newer or older.

Yes and no.  There are fantastic older speakers.  I think what has changed is how many new, inexpensive, great sounding speakers are out today. In addition to those, there are incredible deals to be had on pre owned speakers.  15 year old speakers that were originally $5k are on the used market for $1k-$1.5k.

Computer aided design might give you a flatter frequency response and better dispersion, as opposed to merely listening by ear, but in reality very little has changed.

If things had greatly improved then no one would be listening to old speakers any more than anyone is still using first gen cordless brick phones.

What was the last major across-the-board technical improvement?

I can’t think of any. Boxes are still boxes, cones are still cones, aren’t they?

Look at Harbeth for example, renowned speakers, but still only refinements of the ones that Dudley Hardwood was building 40 years ago. Same for Spendor, Tannoy, Bowers and Wilkins, JBL etc.

Maybe the Kef Metamaterial Absorption Technology (MAT) as used in the LS50 Metas, or maybe not?

We shall see.

In any case, because of inflation, a top $10k speaker from 2008 would still beat most $5k speakers from today, though it would be surprising if they could fetch $5k.