The depreciation in the 4th year is going to be lower, other costs the same (given the reliability of modern cars), except a service and MOT. And the income remains the same. I don’t see it being an extra cost, maybe even a gain.. I’m sure someone will be along to prove me wrong.
I agree on all points. Quids in for Motability, certainly not the other way around.
As an aside, I’m not sure if people realise that when you opt to extend a lease beyond 3 years you do not have to keep it the full 4 or 5 years. You can change at any time you like within the extension period. Obviously you would get the £600 good condition bonus rather than the enhanced one. Quite a good option if nothing particularly takes your fancy in the quarter that you are due to renew. Just extend the lease and then as soon as a car comes on the scheme that you fancy you can speak to Motability and get an order pack.