Just for clarity along with some observations to help ?
IIRC the C43 is the good ladies, I assume she has given you proxy for changes

Which of the cars is she happy driving, any limitations, as that would be a decisive factor.
Also the Tesla seems to be getting a more grumpy description with each post?
However a series of other cars also got booted due to lack of interest in the not to recent past as well? A35, BMW.
The way things are going if you are interested in managing cost you are likely to end up with some form of BEV/PHEV thingy.
The tesla remains hard to beat in so many ways so unless you go up to a Taycan you are not going to see much of an improvement.
If I am honest even if you are currently rather peeved with the V8 I think you love the crazy quotient of a V8 and will never be without some sort of Morgan.
I don't see the CX as automatically newer and better. I think we are seeing the snags already, radiator and brakes, and more will be along.
The truth is they have a limited development budget and price point to hit to avoid killing all their existing customer base.
The good news for the Plus Four/Six owners is that the CX foundation is now under all four wheel models and so issues will be addressed more quickly than our Aero 8's benefited from I suspect?
Low volume and a lack of development was not the Aero's friend.
This will impact on service skills and parts on the road ahead.
If the good lady is happy to drive Aero Plus 8 and the Tesla 3 Twitterbot I would go there.
The C43 will have a better value now than in four years time when the PM has totally hammered road/petrol tax
You have solar panels so maybe invest in a Tesla style wall power pack when this develops into G2H and H2G etc.
Sell them all and get a Taycan 4S Sports Estate, a CX Plus Six and a brick to go under the loud pedal when it's wet.
In truth I am thinking through the same thing.
The S2 and the ML63 are likely to go.
The Mini CooperS R56 has no mileage on it and costs peanuts.
The Coupe is just too pretty to sell but I am watching autotrader to see if the others go for those numbers.
It is due into Williams to bring back to service on the 18th so lets see how big the bill is?
I just don't do the mileage anymore.