I realize that as the rarity of the coin increases, the effect of the cost of gold dropping $100/oz will be minimal. But looking at double eagles, for example, what is the trend? If gold drops a significant amount, will the realized sale prices of Saint-Gaudens drop as well (after a slight lag)?
I think you also have to consider your location as well. I currently am working in South Carolina, silver dollars up here seem to go for around $22 each, while pre '33 gold goes for a sizable amount more then the gold value. Last week I went home to Florida and saw silver dollars are around $26+ each but was able to buy pre '33 gold at its melt value. For an exact answer to your question I think yes it does drop for most of the pre '33 gold
I buy and sell a lot of the smaller old gold coins. I think it makes the prices swing more than it should. It seems like if gold goes down a little, people freak out and won't spend much, but if it goes up a little, my prices when I sell go through the roof.
On common and lower grade material they tend to follow the spot price (with a premium) but they will go up faster than gold when it rises, and lag behind when it falls.