Leather should be worth more then it is now, as it stands its basically a worthless thing to have unless you need it for a mood.
Leather is not useless. It allows you to create cheap, light armor for dwarfs that are not active combatants. If you read the wiki section on speed, you would realize that there is a penalty for encumbrance effecting the agility of a dwarf. If you have enough dwarfs to have a separate military, then it is more beneficial to dress your non-combatants in leather.
I think quadrupling the price of it should be a good start.
Quadrupling the base price, or that of tanned hides, or that of goods made from leather? I do think that there should be a price refactoring between leather, yarn, plant cloth, and silk, but I think quadrupling the price is a bit over kill and would not lead to any sort of balance. Ideally, plant cloth would be cheapest as it is easiest to produce in large quantities and comes from a renewable resource, followed by yarn, then leather, then silk.
Thirdly leather armor should be given better stats as this would give an incentive to actually use it instead of just as a secondary need for bags.
As I mentioned, the benefit is in the lack of encumbrance. There could be other uses for it that would make it more beneficial though. Smithies and furnace operators could wear it to avoid catching on fire for instance.
I think many professions should have a chief noble, such a chief miner. A chief miners job could label which sort of veins are worth mining. Such as all gold veins which have been designated for mining could only be mined by an Expert or higher. A chief miller would be able to designate that only cave wheat be milled. While this may overlap the manager in some spots I think it would be good and give more flexibility. Also I think it would be cool to have more then 1 baron and nobles at a time.
What you are talking about should be wrapped up under guilds due to be released in the caravan arc, though the extent that it will be implemented is unclear at the moment.