There's plenty of perfectly lovely stuff that's extremely valuable and collectible. The observation that once the commoners like something it loses value is simply false.
Quite a lot of contemporary art is unlovely. The common man will never want it for decor, because it's ugly and often much too big anyways. This is because the two roles of 'decorating' and 'meaning' (or whatever description of Art qua Art you like) have been separated. Art need not be decorative, and so, often, it is not.
This is a modern idea. But it is the idea we have now.