The prices are not correlated with the performance of financial markets and the value doesn’t depend by the use on the road, as is the case in the evaluation of circulating cars.
Although it is quite big, a car is not a real estate and it can therefore be transported, for example to be sold to a collector in another country, in a different currency as well.
Cars also combine personal passion, if clients have one in this sense. As specified, classic cars can also circulate according to particular conditions (so, unlike other safe-haven-assets, they also have a practical use).
They can, at worst, be sold even for pieces. In fact, it is less known that, as it is often done with companies (which are bought whole to be sold then in parts, whose value sum can sometime exceed that of the whole company), the total value of the components of a classic car (as spare parts or as collectibles) may even exceed the value of the whole car.