I guess that the biggest overall change across all of the brands has been in cabinet design and refinement, aiming to minimize energy storage, and keep them quiet.
Sound quality of Newer versus Older speakers
From a sound quality perspective, is there anything that newer speakers are doing better than older speakers. For reference, I have a pair of Monitor Audio Silver 300s which are amazing me with their ability to balance detail retrieval with an ability to avoid harshness (with the right ancillaries). My subjective perception is that this type of balance between resolution and refinement was more difficult to find in speakers from 20-30 years ago.