Common date gold coins are also referred to as Generic gold coins. This is due to the quantity of coins that exist in the market place. These coins are readily available and are traded as like-kind units instead of as a specific coin. Therefore they are less expensive than the better date/rare gold coins. The value for common dated coins is primarily derived from the gold content and values tend to ebb and flow with the spot price of gold. The value for better dated/rare gold coins is determined by quality, rarity and availability. The gold content in better dated/rare gold coins is a secondary factor in the value.
Common date gold coins are available in $1, $2.5, $3, $5, $10 and $20 denominations. This is not the value of the coin but rather the denomination assigned to it when it was originally minted. Gold prior to 1933 was set at $20 per ounce, so a $1 coin was 1/20 of an ounce and a $20 coin was one full ounce. Common dated coins come in the Indian Head design from the $1 to the $10 issues, and then the design changes to the $20 Saint Gaudens design. Liberties are available in all denominations. The most common $20 Liberty is the 1904 Philadelphia mint and in the $20 Saint Gaudens it is the 1924 Philadelphia mint.
Generics are typically slabbed in plastic holders in the higher grades in the same way that rarer issues are. They can range now days in the $20 Saints and $20 Liberties anywhere from $1,400 to $6,000 depending on the grade and particular dealer.
Common date gold coins are typically used for their gold content plus a small numismatic premium which makes people feel as though they will not be confiscated. I have read that the Patriot Act III requires the value of a coin to be at least double its gold content to be considered non-conficateable, but I am not positive if this is absolutely true. If this is the case then some common dated coins would not be exempt from confiscation.
Common date gold coins can be a great addition to any well diversified coin portfolio, however it should be noted that rarer issues have performed better in the past.