You can still get most of the bits for a Series 1 and they haven't made those officially for ages. So I'm not expecting Defender spares to be a problem in my lifetime.
As to the value of complete vehicles, it's hard to say. Certainly looking at Ebay and Autotrader, nice shiny examples of recent vehicles (last 10-15 years), especially County Station Wagons seem to be commanding high prices still. So that may well continue.