Why get obsessed with values of Morgans? You would not buy a BMW, Jaguar or any other so called premium car if you were worried about residual value.
The days when Morgans were an appreciating asset are long gone with some notable exceptions, the market for so called traditional Morgans gets smaller & smaller all the time, the people who want one probably already have one, many are now sold on behalf of a deceased estate check the auction sales.
I have had my Plus Six for 3 years and considered a new 24 year model. The cost to exchange was ridiculous and for what? The performance is the same, I don't need air bags, traction control and the new roof robs me of shoulder space, so I will stick enjoy my car and not worry about what it's going to be worth in 5 years time.