That is impossible to answer objectively
setting aside all the inevitable and highly variable and totally subjective and biased personal value judgement suggestions, it is analogous to asking..
Q "How long is a piece of string ?"
A "it depends "
in in this case it depends on timing, location, and other esoteric factors such as emotional attachment or its converse, and economic influences and technology obsolescence
For example, when the next inevitable / looming recession finally hits with a vengeance, the current market values of all will decline appreciably. Some will even crater, independent of any other affection for the unit.
A second example is the ever changing and accelerating technology advancements . There are plenty of quality build high-end brand products in excess of $10K when new , that have a market value of a small percentage of new within 2 years. Let’s remember that a 50% drop in the first year of most product is quite common , full stop..... INCLUDING 2-channel. The litmus test is see what you can actually get on a dealer trade-in or compare against the "solds" in audio forum ads.
Be prepared for a sobering gulp even in 2-channel ...just like in luxury cars obsolescence.
AV is a subset herein and the worst subset by far that needs little discussion intuitively. For example, many AVRs and processors will not be even be taken in on a dealer trade-in and are little better than boat anchors in the resale market.
Simply put, anybody who :
(a) contemplates buying gear driven by a thinking they can successfully hedge against depreciation in an ultimate contingent and variable future price arena; then
(b) they are unnessarily shortchanging themselves for best available performance now, and
(c) myopic to a fault and still being exposed to a rude wake-up call disappointment -- and likely shock-- if the current equipment line-up is line for change....
full stop.
