Stick to long-term investing and you'll be thrilled with Costco stock.Costco (COST -0.44%) stock is an investor favorite. It's a reliable, market-beating stock, and it pays a dividend, has a self-generating revenue model and plenty of expansion opportunities.Wall Street analysts, though, don't see too much upside over the next 12 to 18 months, possibly because the stock keeps climbing and has become highly valued. But you might want to consider buying it anyway.The self-generating revenue modelI don't think ...