Of course, all treasure is not in precious metals or rare or finely made substances. Is not a suit of armor of great value? What of a supply of oil? a vial of holy water? weapons? provisions? animals? The upper levels of a dungeon need not be stuffed like a piggy bank to provide meaningful treasures to the clever player character.
—Gary Gygax, AD&D Dungeon Master’s Guide
Old-school adventures are full of junk. Treasure troves don’t just contain precious metals in thousand-coin increments! There’s all sorts of other valuables: furs, furniture, jewelry, silverware, casks of wine, wheels of cheese, and any number of other knick-knacks, many of questionable value.
This smorgasbord of variably-valued valuables serves two functions. The obvious one is verisimilitude; an interesting array of treasure helps make clear where the dungeon came from and gives a sense that the treasure is there for a reason. But many old-school play groups aren’t concerned with simulating a living world! So why should they bother?
Such groups can get mileage out of the other reason, which is that unusual treasure poses a challenge for the players. Any dunce of an adventurer knows to take the gold coins and leave the copper ones. But which is more valuable, the silver-chased coffer or the mahogany chair? The fancy porcelain serving dish or the collection of scrimshaw? You can only carry so much, so what do you take and what do you leave to be despoiled by the dungeon’s other denizens?
More importantly, unless the DM adds a selection of minor valuables, the major ones shine forth as blatantly as diamonds on black velvet. If every trove contains nothing but gold, gems and jewelry, the moment the PCs find a carpet, censer, girdle, horn or mirror, they’ll know it’s some sort of miscellaneous magic item. Don’t just give the show away with such transparency. Make them use precious spell slots to prepare detect magic!