The chart above is a 1970 to Date Chart of Key Dates and Rarities in an Index. The Index clearly shows record all time high prices every year since 1998.
The coins represented by this Index increased in value 9,523% since January 1970. That’s 3,057% more than the coins represented on the broader CU3000 (PCGS3000™) Index. This significant difference in performance is primarily a result of quality coins (Mint State) coins outperforming the overall market. By contrast, a subset that represents lower-grade coins, the Generic Gold Coin Index, is up "only" 2,775% since January 1970. By comparison, The Dow Jones Industrial Average has risen 1,340% since 1970 (adding dividends would make that figure higher).  Also revealing the difference quality and knowledge can make, as of December 31, 2005 another subset, the Key Date & Rarities Index, is up 66.42% for three years vs. 18.25% for the overall CU3000.  Understanding The Rare Coin Market