It makes me laugh when i see these cars for sale, with huge lists of all the mods that have been done, invariably with the words "worth £xxxxx"after each mod.
Just because a mod might have cost a lot of money, doesn't mean it's worth a penny unless a buyer wants it. The more a person mods a car, the more they are tailoring it to their own preferences and away from what others might want.
Just my opinion (which is worth two penn'orth, BTW)