First let me say...I really do like properly designed and well built Ferro-Cement boats and, from what you say in your post, this boat is definitely a well designed and built boat!
You say the PO had a plastering team fly-out from Hartley, New Zealand, to plaster the boat, (Wow! Now that cost alone could have bought the builder a second-hand plastic boat
) so that tells me that your Dad's mate did not skimp on the build. (He must be worth a few bob
) You also said, the yacht has all the Lloyd’s certificates, great! You can bet your life, (and you will be betting your life, all folk of the sea do so every time they go to sea) your FC boat HAS been properly designed and built to specifications...Even though I believe, at 50,000GBP, your paying way to much for the boat.
Similar well designed/built FC boats can be found in AU and NZ for 35,000 DOLLARS and upwards, depending on size, and FC boats are much cheaper in the States but then, a boat, any boat, like anything else second hand, is worth only what a buyer is willing to pay for it.
You said the boat is a Bilge Keeler. i.e. You can sail up to a beach at high tide and wait for the tide to go out, leaving the boat sitting upright on the sand, then walk ashore. So the boat is shallow draught, if that is so, perhaps you could nip over to France, enter the French canal system and go down to the Med using the canals. It's been well over forty years since I've been in the Med and I entered from the North Atlantic, I was told of the France/Med connection by other seamen in the local Greek bar, so perhaps others who have used the French canal system could advise you better on that system.
Good luck with all your plans Ant.