I agree with the approx. £200 on resale premium for leather but, done tastefully, it makes the car that much more desirable and therefore easier to sell on - that COULD add another £200 at least to haggle for. More to the point is the pleasure it gives while in your tenure.
Allan has six hours to kill in Rotherham - sounds like a bit of a life sentence!
Suggestions :-
Library - plenty of upholstery reference books to read up on - followed by a matinee performance at the cinema - perhaps 'Car Wars' ?