So the retail hi-fi industry is designed to get people to ‘trade-up’ to new, often inferior equipment..?

Sadly, yes.

Just ask the owners of newer NAD or Cambridge Audio gear how they felt when their expensive equipment died after five years or so.

Read the reviews. Every new piece of gear sounds significantly better than the one preceding it. How then is it possible for a 40-year-old amplifier to sound better than a new one? What about all the advancements..? If each year brought significant improvements, older gear would have to sound awful compared with gear with 40 years of continuous improvement, but it doesn’t and this should tell you a lot.