That's just obscene... Of course it makes sense, they grab whatever item is closest, which will inevitably be whatever item they worked with last.
This. This mechanism is why I rarely make shitloads of stone crafts anymore. I can generally get a gem craft at random and encrust it with everything under the sun. Or I use metal crafts when I just need to get rid of all this FUCKING GOLD.
Leather crafts aren't worth all that much.
You'd probably want to start out with a valuable material and then make a valuable item out of it, like a mechanism or a statue. Then decorate the hell out of that one item. Once its all decorated you can put it in a room for dwarves to admire.
You lose the ability to sew an image onto it, so you lose one decoration, but the base value is far higher.
...A skilled clothier can make GSC items that are more valuable than anything sans HFS)...
...Too bad you can't make GSC Silk Serrated Disks...