Component obsolescence

How long does anyone own a component before considering it obsolete? Technology improves but how fast?
For example,I've heard that old Dynaco amps are still considered good. Or Japaneses receivers from the 70's are good by today's standards.
Would speakers and CDP be the fastest changing components? How easily could an Aleph P preamp be significantly improved?
Maybe a lot of our monthly component switching (speaking for myself) is for a different sound, not always improved sound?
And then, what does anyone do with their 1988 Adcom power amp? Is there even a market for old stuff?
Cdc, that's a lot of questions, but I'll take a stab at them in order:

1) Depends on the someone and on the component; anything that still provides enjoyment to anyone is not obsolete.

2) & 3) Technology moves at different speeds at different times for different aspects of sound reproduction. It is often driven in response to something else, as digital currently is being driven by new source formats and the analog resurgence. Sometimes something old becomes new again, as in the SET phenomemon. But I would say the most significant technological changes over the past 10-15 years have most greatly affected the performance of speakers as a class. This has mostly had to do with the wide and inexpensive availability of powerful computing capabilities to aid in the measuring and modeling of speaker performance. And a lot of alleged tech improvements really just boil down to marketing when looked at from the perspective of hindsight.

4) I too do not believe that any very significant improvements are somehow waiting to be made in areas such as SOTA preamps, for instance. Today's good preamps probably represent one of those components that has really improved dramatically in the past 10-15 years as well, to the point that further gains will likely be small, or not focused on sound quality per se.

5) Maybe so...I wouldn't know! ;^)

6) & 7) There is always a market for boat anchors...
Obsolesnece only applies to Digital(DACs keep getting better and cheaper all the time) and to computers which are obsolete before they hit the MFG floor.
I'll answer your last question - you give it to a friend or relative who has never had anything nicer than a low-end receiver but who might be interested in something better if they heard it. Or, you establish a very modest value for it, and donate it to a charitable organization to put sound in a place that might not otherwise have it, and take a modest tax deduction.
Well, except for the age associated degradation of cetain internal parts, the unit will sound as well as it ever did when it was new. If you replace these parts, like the capacitors primarily, you can keep the majority of the original sound. If you like that sound, there is nothing wrong with staying with it. Some people might like that "older" sound quality better, and I would not judge that. I do think that sound quality has gotten better with technology improvements over time with alot of components, but not everyone may agree with my opinion on that(or anything else, for that matter). But some stuff, like the great phono sections from the 80s continue to surpass the new stuff, except for certain megabuck ones. But you must maintain them, if you want to keep the performance.
My experience is that many older designs can easily hang with current designs IF the "technology" of newer passive parts ( resistors, capacitors, diodes, wiring ) is brought up to date. Most of the "improvements" in audio products have not come about because we have a whole new way of designing gear, it is because we simply have better quality raw parts to work with. There are plenty of "old" designs out there that measured phenomenally well, were wide bandwidth, offered excellent transient response, had low distortion without gobs of negative feedback, etc... Finding these and updating them can give you world class performance for pennies on the dollar and the cost of new parts and some personal elbow grease.

As to things that DO "fall by the wayside" quickly, start looking at various surround sound processors. Dolby Pro Logic processors are selling for anywhere from 10% to 20% of MSRP when new. That does not mean that they will not work, but simply shows that there is very little need / desire for them.

So long as something functions as intended and someone will use it as designed, a product is never "obsolete". It is just not "highly marketable". Sean
Thanks for the interesting responses.