If you invested $10,000 in warehouse-style retailer Costco Wholesale (COST -0.70$400,000 today. Simply put, Costco stock was a life-changing investment for some investors thanks to its incredibly consistent performance. As stellar as returns have been for Costco, one current risk unsettles some investors: It currently trades at a price-to-earnings (P/E) valuation of nearly 60. That's its highest valuation in over 30 years even though its growth prospects have cooled considerably ...