There has been really no improvement in the overall technology of speaker design in decades. What has been improved is the reliability and durability of the components used to make top quality speakers. As an example Quads have been around since 1956 and people loved them but they were notoriously unreliable and fragile. In the late 70s Acoustat developed the first bullet proof electrostatic speaker. You have to attack the speaker with a spear to damage it. Sound Labs took the concept even farther and they have been at their current performance level for some 20 years.
Buying used vs new speakers from a technology perspective
Do you believe a speaker's components like drivers and crossovers can become "outdated" for lack of a better word? For instance say someone is selling a pair of speakers that cost $10k in 2008 for $5k now. Comparing that speaker to a modern day $5k new speaker only looking at driver design/drivers, cabinet construction, crossover components/layout and other materials what kind of technology gap are we looking at?
Have there been technologies or designs that have come out in the past few years that you couldn't live without after hearing?