A value drop is not what defines a Ponzi scheme.
In Ponzi schemes it's certain that someone will lose, because there is no other way.
E.g. Buying an old painting isn't one. There are people with a lot of money that appreciate this art and want it.
Sorry but its not really true. I saw nice paintings that are very cheap only because its author is still alive or not known. Also someone can just paint another copy of expensive painting and it will be worthless. Why? Because something else is driving the price. To me this is exactly like ponzi scheme.