In the dotcom bubble overvaluation was really focused on tech. Something interesting about the market recently is the big tech names are performing much better. AAPL MSFT etc. As this chart shows.
The S&P500 is weighted toward larger market cap companies. The equal weighted index is what it would be if all companies were weighted equally. So the ratio S&PEW/S&P (red line) declines if the larger market cap companies are doing better than the smaller ones.