Desirability is just as important if not more than rarity. They don't always go hand in hand.
Something which is big, saw little use and to the guys who like dressing up hard to portray accuracy, limits the market.
Having said this looking at the silly prices which are being asked for a lot of British vehicles at the moment, providing it needs no major work, you would like to think it may reach £15,000 to £20,000.