I had to go back to the first post to remember what the topic actually was. Fine - it was wide open.
Firstly, let me be honest and say that I have very little user-experience of the wide variety of available stuff of any period. I had neither the funds, nor mercifully the need - as an EE I could design/build my own electronics; acquired items were a Thorens TT and Cambridge CD and tuner of rather later vintage. Loudspeakers Philips trios in home built enclosures.
That said, one must keep in mind that manufacturers probably paid attention to demand. In whatever period, hi-fi was never that lucrative that manufacturers could ignore quality as well as taste - and that was true as long ago as the post WWII period of Leak, McIntosh, Quad and similar. Several other posts indicated the ups and downs in other factors, so that in the end production/sold quantities were as much influenced by whatever factors reigned at any period as quality only. Three substantial factors among many more were the advent of semi-conductor devices, home theatre - and, as always - "the Jones's"!
From a technical point of view one has to remember that the height of development/advance in tube equipment was probably the 80s, when the convenience/allure of mass production of semi-conductor stuff started throttling demand for tube-based equipment. This was also a time where the former was still plagued by misunderstanding of the technology etc., rendering equipment of poorer audio quality than somewhat later years.
After that ..... human hearing did not improve with the years (often rather the opposite as a result of ambient factors!), and what was inaudible in the 80s is still inaudible at present. To me development was rather 'horizontal': Hosts of convenience and features which rather doubtfully influenced the audible signal itself, actively helped along by floral promotion featuring an ever increasing degree of nonsense parading as 'facts'.
But that is somewhat off-topic. I would roughly make the sweeping statement that the 80s could well have been somewhat of a peak in what was on the shelves - if such a statement has any value in describing 'real' value. (One might as well try to establish what/when was the most lucrative period for jewelry ......oops!)
And then there were cable 'advances' ......
