I suppose I should have said "things that have importance to large numbers of people". That wouldn't include personal possessions. People always think their stuff is valuable simply because it's theirs. I've expertised paintings whose owners believed, or wanted to believe, they had a lost masterpiece. Every once in awhile, that happens, but it's rare. Nothing I ever had to break the bad news about was worth much of anything. Same goes for real estate; I gather from what I see on HGTV that many people want to believe their homes are worth more than they really are, even though there's plenty of information about the market available.
But that wasn't what I meant. When something is important to a lot of people in a certain place, there's a market for it. And that will sustain, and perhaps drive up, the price. That's what markets are about. The Dutch love flowers. They do a great deal of international business in cut flowers, delivering them all over the world daily. But ordinary people love them too; there are weekly flower markets everywhere, and everyone seems to buy a big bunch or two.
So perhaps they were particularly vulnerable to the tulip craze because of that.