In an article published at Seeking Alpha, Jeff Clark argues the gold trade is not crowded. He uses a figure calculated by John Paulson, which divides the total amount in gold ETFs (at $1,200 gold) by the total amount available in money market funds. The ratio is only 2.7%.
Clark points out the gold trade seems crowded because gold assets and interest are high relative to the dearth years. That said, he notes an increase in the above ratio to 10% would cause the price to explode.