You should be able to use a forge to melt down gold items and turn them into gold pieces.

Gold is a metal associated with the sun, so weapons made of it should deal extra damage against undead. Additionally, blunt gold weapons get a d2 damage bonus versus everything due to being heavier.

Gray philosopher’s stone; a randomized gray stone that turns objects (possibly only of a certain material) rubbed on it into gold if non-cursed, and turns gold objects rubbed on it back into that same material if cursed.

Piercing weapons never generate as gold, because gold is a terrible material for maintaining a sharp point. Either that, or using a gold piercing weapon to attack things regularly decreases its enchantment.

It’s harder to force the lock on chests or large boxes made of metal, and increases the chance your weapon breaks. Additionally, the material of the weapon used to force the lock affects the result, if it’s used to pry rather than bash:

• Iron and metal behave as normal.
• Mithril is stronger than iron, and breaks less.
• Copper is slightly weaker than iron, and breaks a little more often.
• Softer metals, such as silver and gold, break less often but tend to bend. A “bent” weapon doesn’t actually become bent internally; it just loses a lot of enchantment.
• Wood is about as good as copper.
• Glass almost always breaks, and can break even if used to bash open a lock.

Croesus generates wearing a random gold amulet (probably not change or strangulation, though).

Change one of the existing boring wand descriptions to “gold”, and make its material gold, for the purposes of being stealable by leprechauns.

Crude (orcish) items should never generate with valuable metals (gold, silver, platinum, mithril) as their material.

Engraving with a blade made of softer metals such as gold or silver should dull it faster than an iron blade.

If you tell a vault guard that your name is Croesus, and you are wearing gold armor, they might lead you out of the vault without forcing you to drop any gold. The chance of this outcome increases for each piece of gold armor you are wearing.

Hitting monsters that have a passive shock attack with something made of copper, silver, or gold increases the amount of shock damage.

New Medusa-alternative level (like the Grue and Echo levels in dNetHack): Chrysaor’s Palace, containing a fair amount of water, soldiers, and Chrysaor, who wields a +10 gold broadsword and a gold shield of reflection, and whose attacks and resistances are on par with Croesus or even better.

Make Sunsword out of gold.

Object materials: cursed gold items cannot be dropped.

Wearing armor made of gold increases your Charisma by 1 or 2 for each piece worn (possibly even bypassing racial maximums).

Gold objects deal extra blessed damage and extra cursed damage (i.e. extra damage from wielding a blessed weapon versus undead will be enhanced if the weapon is gold).

Leprechauns (or anything with AD_SGLD) should steal items made of gold out of the hero’s inventory.

Carrying gold items openly causes leprechauns, dragons, and Croesus to be automatically aggravated.

Leprechauns steal anything made of gold, in addition to plain gold pieces. (In vanilla, the only gold item is the gold ring, but variants have other gold items.)