The S&P 500 is up almost 15% in the past year, although just 3% year-to-date—after recovering from the March COVID-related downturn. Some market gurus think the market is getting overheated. The P/E ratio (Price/Earnings) for the S&P 500 stands at 28.8 today, and that is considerably higher than its historical 15.8 average for the past…