The second-quarter earnings season is off to a ripping start, with consumer strength powering resilient corporate profits. In the stock market, however, the reaction has been fairly quiet, an ominous sign that much of the good news is priced in — and investors are punishing disappointments.

With Wall Street's surge to record highs, the U.S. stock market looks nearly as expensive as ever, and investors are debating whether the lofty valuations are a bearish signal or justified by the technology-heavy market's profit outlook.