Great thread indeed. I think we should distinguish the personal (generational) point of view form the historical one.
As for the latter, for instance, there exist museums of XX century technology which are already dealing with the problem of obsolescence of the electronic components: the same that interest former, that is, ourselves!

Not an easy task, given that mass products have been more and more conceived in such a way to deteriorate quickly (especially from the 80s on).
I agree with Chris that the plastic cases are the most vulnerable parts of boomboxes (electronic components may be available for longer, although the question of 'how much longer' is debatable). I think that both can be surrogated when the 3-D print technology will be perfected. It's already advanced enough to be able to duplicate entire buildings: I read somewhere that the archaeological ruins in Palmira (Syria) can already be rebuilt with super-professional 3-D printers (it's a long process, but it's already possible).
As a footnote, I think that we, as collectors, already contribute to the preservation of an aspect of cultural and material history of our times (70s-to date). We do it already at all levels, from finding a solution to a practical problem to saving units from oblivion. I'll just add that I've often thought to donate my collection to a museum one day. This is precisely because I like the idea that future generations may have access to the memory of an age that is not already past and yet in danger to be forgotten.