The viability of the horse business hinges on a precarious equilibrium. Its values have to work out often enough for the rich guy to keep spending, but not so often that the rest of us have to pack up and go home. Very seldom, however, are both extremes embraced so proximately as by Meg Levy last weekend. On Sunday, the Grade I success of Valiance (Tapit) in the Juddmonte Spinster S. vindicated all the promise, in pedigree and physique, she had evinced as a $650,000 yearling sold through Levy's Bluewater...