I stumbled upon a wonderful explanation of why magic item creation in D&D 3.5 requires Gold. Now typically, I think the game generally assumes that the gold is spent on rare reagents used to create the items, but this version told it differently. Gold itself is magical. It provides a base for the spells that provide the item's enchantment.
I saw this, and I liked the general idea but didn't think much about it at the time. Recently, it came to mind when I was writing a fantasy adventure. What fantasy creature is known for their magical power and their love of gold? Dragons.
A Dragon's horde is necessary for proper growth. Without a large supply of gold to nest on, dragons grow into the small, stunted, neotenic creatures called drakes. If a dragon only gathers a small amount of gold, they grow in size, but do not develop the intelligence or magical powers of a dragon. These monsters are known a wyverns. The wyvern's great size comes with some major changes from the normal dragon phenotype. The front legs gradually fuse with their wings and their tail grows a deadly poisonous stinger.
The changes in wyverns are not the only example of physiological adjustment induced by gold. All forms of dragons change slightly when they receive the proper amount of gold. The famed fire breath of a dragon is an adaptation induced by proper nesting. Dragons that make their nests near water eventually develop gills to adapt to life below the waves. If a dragon nests underwater, often in or around sunken treasure galleys, their limbs shrink and their tail elongates. The legs become fins and the tail grows a single ribbon-like fin, much like an eel. These aquatic dragons are better known as Sea Serpents. Despite the great change in body type, these creatures started out as the same four-legged creature as any other type of dragon.
Nesting in gold does not only provide fuel for the creature's growth cycle, but it sustains them in other ways. A true dragon requires magic to sustain its body. Typically this is obtained through long periods of nestled in their horde. A steady diet of magical beings, such as wizards, could substitute in a pinch. Underdeveloped dragons don't need the same amount of magic to sustain their bodies, if they need any at all. The diet of neotenic dragons is entirely carnivorous. For true dragons, while they may eat meat (particularly livestock), any non-magical food they consume is for pleasure alone.
Like with magic item creation, the process of nesting consumes gold slowly. As such, dragons must always be looking to re-stock their larder, so to speak. Tribute and raiding do an adequate job, but dragons more in touch with the affairs of humanoids may kidnap royalty in order to extort a ransom, hence the tales of dragons stealing princesses. This also has the lovely side effect of attracting rich knights and other adventures, including tasty wizards which can provide a nice dietary supplement.