Hi,
I'm sorry but I think you need to get real about what your Mini is worth - it simply isn't worth the £20,000 you are asking...........a GP it is not.
I won't comment either way on the "special" mods but I don't think they add any value to the car.
There is a 54 plate factory works convertible on Piston Heads with much lower mileage and higher spec than yours in the very popular dark silver for £17,000.
That is a far more realistic price and that particular car is unmolested (according to the description, pictures someone..........
).
Certainly a "unique" Mini you have there - good luck with the sale..