Even a common as muck bog standard machine now could be worth a lot in the future - purely because they are so common. No-one nowadays would dream of saving one for the future. Its often these models that die out completely in years to come. In the UK, a good example would be the Dyson DC07 - in its day, every Tom Dick and Harry had one, and they still do now in some form or the other, usually buying them reconditioned. But in 25 years time, how many people will still have a mint DC07? They will all have been scrapped years back, no-one ever thinking that they will be rare one day.
Take the UK Ford Cortina, in the 1960's they were everywhere, and I mean everywhere. Now, 50 years on, they are worth an absolute fortune. Even common 80's cars like the Ford Sierra are so rare now, that they have all but disappeared, and they are already getting highly sought after, especially the early 80's ones.
So don't dismiss saving some models of what you Americans consider Walmart throwaway vacs. Many people will remember them in 2030, but who will still own one? and who will actually own an unused one?
Contrary to what we might think, brand new rare models now, TOL expensive models or unusual models WILL be saved, as people will EXPECT them to be rare in the future, so many more than you might think will survive the test of time.