"Through Wednesday’s close, it’s been 507 trading days since the last record finish for the S&P 500, according to Dow Jones Market Data."

Kinda what you'd expect from these type of valuation levels?

As of today, you could purchase a 1 Year T-Bill that will return 4.8%, a sleep easy, boring, (I like boring!) no stress return.
Or you could purchase the S&P 500 with a P/E of 25.7 and an earnings yield of 3.88%.
Currently the price to book on the S&P500 is 4.4. Just for perspective of what could be: 2009-2012 it was bellow 2.
I also like to keep an eye on the 'Buffett Indicator' (ratio of total market cap to GDP) which Warren has described as, 'the best single measure of where valuations stand at any given moment.'
It currently stands at about 175% of GDP.
"If the % relationship falls to the 70% or 80% area, buying stocks is likely to work very well for you.
If the ratio approaches 200% as it did in 1999 and a part of 2000 you are playing with fire." ~Warren Buffett

Lastly, starting from valuation levels similar to what we have today...
over the last 100 years the S&P 500 took three long, interesting trips to nowhere,
underperforming risk-free Treasury bills for 53 of those 100 years (1929-1945, 1959-1982, and 1995-2009).

All #'s taken from Schiller's site:

multpl.com - S p pe ratio

marketwatch.com - S p on track for first record close in over years is it time to celebrate