Opportunity cost
The money would be better spent elsewhere I'd suggest. Whilst I'd agree that maintaining one of these beasts as a static display would be preferable to junking them both, I'd offer the opinion that maintaining even one in operational condition would be a gigantic waste of money. These are cross-Channel ferries! Imagine one trundling round Duxford...
I well remember the introduction of the first few hovercraft. They were hailed as a British revolution in transportation (British!) that was soon going to be seen in all kinds of applications. I also worked for a while with a woman who had been a hostess on one of these craft. The most lasting impression it left on her was the quantity of vomit she had to work around in less than perfect weather. No doubt there may be a few residual applications in the military where these craft are still extremely useful but in the main they were a technological cul-de-sac.
Now the "Caspian Sea Monster" Ekranoplans is a different matter. I'd pay for a trip round the bay on that.