Game-based virtual property is something I'll have more to say about in the future. It might give us some insight on how other kinds of purely or primarily online property may develop. Of course, game-based virtual property is no more "imaginary" than any other kind of property. Its value, like that of any other property, is based directly on the various preferences people have for it, as well as well as on its supply, and only indirectly on attributes of the property on which those preferences are based. Those attributes may be tangible or intangible.
One interesting issue for game-based property is whether inter-game trade in it ruins the sport of the game. Imagine, for example, if in baseball the New York Yankees could buy not only bid for the best players, but could directly buy bases. Or even just barter bases between games. Imagine the Texas Rangers allowing the Yankees to turn a double into a home run, in exchange for two extra runs for the Rangers in a Yankees-Rangers game next year, so that the Yankees could beat the Boston Red Sox this year for the eastern division title.
A "level playing field" that is considered necessary for sports to be "sporting" seems to require various restrictions on trade. The goal of a sport or game is typically not efficiency in scoring runs or accumulating "gold pieces," but entertainment.
Many people justify trade restrictions outside the realm of sports and games, where efficiency is quite important, on the same kind of ethics. The results are often wasteful, and sometimes disastrous.