On SO at least, users usually ask questions when they have a real problem and they need a real solution.
If you change the motivation from needing an answer to wanting a badge, the thought process can turn from:
"I have have a real question that I can't find a real answer to."
to:
"What questions can I make up to earn these badges?"
I hope I'm not the only one who can see the second case would very likely lead to a rapid fire of quick, pointless questions. The badge hunter who asks them isn't really invested in the question. They have no reason to care if the question gets answered, all they care about is moving closer to the badge.
Do we really want to send the message that users should be asking more questions that they don't really need answers to?
Is this the kind of participation we want?
We optimize for pearls, but you still need plenty of oysters.
A quick note about optimizing for pearls...
From: http://en.wikipedia.org/wiki/Pearl
Almost any shelled mollusk can, by natural processes, produce some kind of "pearl" when an irritating microscopic object becomes trapped within the mollusk's mantle folds, but the great majority of these "pearls" are not valued as gemstones. Nacreous pearls, the best-known and most commercially significant pearls, are primarily produced by two groups of molluscan bivalves or clams. A nacreous pearl is made from layers of nacre, by the same living process as is used in the secretion of the mother of pearl which lines the shell.
So... While almost any shelled mollusk can produce some kind of pearl, it is really only certain kinds of shelled mollusks, those lined with mother of pearl, that produce pearls that are actually valuable.
Lets think about ways to cultivate questions lined with the kind of quality that will hopefully generate real valuable answers rather than trying to simply cultivate more questions.