The S&P 500 is up about 18% compared to this time last year, and plenty of investors are enjoying big jumps in their portfolios. But that doesn’t automatically mean everything is great. Some investors fear the market is getting too expensive. When stock prices rise faster than company profits, it usually means emotions are pushing prices up — not actual performance. And that can make the market more vulnerable to a pullback. Must Read Plus, there's a fair amount of instability in the economy right now. ...