If anything, the forward returns on stocks and bonds (well, stocks anyway) are HIGHER and BETTER after the events of the last 2 months. Hell, they were best on March 23rd at S&P 2,200.
I respect Mark's opinions on grading and coins, but when he tries to make an investment case for coins and collectibles based on stock market volatility, let me off the train. He'd be on more solid footing predicting a rise in gold to $3,000/oz dragging up coins than an investment case based on volatility of other assets that pay income and dividends.
Reading RWB's book on Saints with extensive price history from 1976-2015, plus my own research over the years, confirms that even if the long-term and rolling period (more important !) returns on coins/collectibles were positive and/or closer to stocks or a diversified portfolio of financial assets....the positive returns are so concentrated in a few years of gains that the inevitable market-timing means most people will not only lose but lose big.