Leather crafts aren't worth all that much.
It depends on the beast the leather is made from. Hoary Marmot Leather crafts aren't worth much. Giant Cave Spider Chitin crafts are, though it's not worth as much as GSC Silk(Then again, what is... A skilled clothier can make GSC items that are more valuable than anything sans HFS). Of course, I think GSC Chitin is bugged and thus unavailable in 0.31.03, so it's a moot point.
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.
Not sure if it is a bug or not, but Serrated Disks and another trap component... Spiked Balls I think, are worth obscene amounts in the new version. They have a 128 multiplier, compared to furniture & craft's 10, statue's 25 or mechanism's 30. I don't think you can encrust them with gems, but you
can stud them with metal at a forge. Layer a steel disc with gold, platinum, aluminum and you will have one extremely valuable object.... Even no-quality would be worth 17,920☼, while masterwork would be 215,040☼!
Too bad you can't make GSC Silk Serrated Disks...