(ChicagoTribune) - If the secret to investing is buy low and sell high, the steep drop in fine wine prices, down between 25 percent and 40 percent from a year ago, could be an opportunity to diversify a portfolio -- or not. "I think there's plenty of air left in this bubble. There's more of this drop to come," economist and author Robin Goldstein said on the sidelines of the American Association of Wine Economists' (AAWE) annual conference at Princeton University last week.