I think placing gems gives more for dwarves and gnomes (or your campaign's equivalent) to do.
Whenever I place gems, I try to keep in mind:
1)Value of the stone -the more valueable, the more likely they are to hold on to it for an extended period of time...which lets me write plot hooks involving it.
2)Legends associated with that type of stone...which lets me write plot hooks involving it.
3)Legends that could be associated with a PARTICULAR stone, like the Hope diamond...which lets me write plot hooks.
4)My players- because some of them are just as aware of those legends, or because some of them just love gems...which can ALSO affect plotlines.
Examples:
Amethyst is associated with Dionysus because of its deep purple color, and as such, is ascribed the ability to ward off drunkenness.
Opals are among the most beautiful of all stones, and come in a wide variety of types. All are soft, some are valuable, some aren't...but there is a superstition that it is unlucky to buy them for yourself- they should be found or given.
There are many kinds of gems that can be found in meteor strikes- diamond, peridot, some precious metals. Some mineral finds are even "unique" to meteor strikes, like crystalline-structured nickel-iron. Any kind of stone found at at meteor strike will likely have mystical powers ascribed to it, and that crystalline nickel-iron is HARD stuff- I have an engraved piece (for jewelry) that broke 3 diamond drill bits (not the diamonds, the steel in which the diamonds were set) during the engraving process. Something like that would be highly valued by armorers and weaponers. (I did have a suit of Plate made of that stuff for a PC in a campaign I was running.)