There are two differences. One, gold is impossible to counterfeit. The Fed can print more money, companies can dilute their stocks, Topps can introduce new lines of baseball cards, but short of building a particle collider, you can't make more gold. The chance of a new discovery affecting the price of gold is rather slim. The Earth is pretty well explored at this point. The second difference is that gold is a natural Schelling Point (http://en.wikipedia.org/wiki/Schelling_point). Society needs one object to serve as a store of value. We call this object money. Throughout the ages, this object has consistently been gold. Currently, we are in a historically abnormal period where the store of value is a U.S. Federal Federal Reserve Note. If it looks like the U.S. government is abusing this privilege by diluting the currency, people start hedging back towards gold. On the other hand, if someone like Paul Volcker starts running the show, faith in the dollar is restored, and the price of gold collapses.
So yeah, gold is like the ultimate baseball card. But the emphasis is on the world "ultimate", and that makes all the difference.
2 reasonably big assumptions:
1 stable supply (no new gold)
2 stable as a Schelling Point. Not unreasonable. But it's not unreasonable to assume the dollar will maintain value either.
Society needs one object to serve as a store of value
Unfortunately, it does not have one. Gold is one such object. You yourself are describing a fluctuation in demand in response to US government actions. That will lead to a fluctuation in price regardless of the real world value it supposedly represents - just like any other currensy. With the bonus that you can make earings out of it.
Exactly, gold fluctuates like any other currency. The disadvantage with gold is that you can't earn interest or dividends in it. The advantage of gold is that it is run by the most responsible monetary authority in the world, a central bank that couldn't print more of it if it wanted too. Pros and cons, to both, that's why the suggestion is to keep about 25% of one's portfolio in gold. It's a hedge against a gross mismanagement by the U.S. government.
So yeah, gold is like the ultimate baseball card. But the emphasis is on the world "ultimate", and that makes all the difference.