I know that I'm a bit of a broken record on this point, but I think that we really need a more deep system of refining resources for non metal materials.
The main resources can divided in those 4 categories:
Currently, the metal is the one best characterized. It requires a facility to process it (land area cost), it interacts with other resources (Fuel cost), it requires time (time cost). This complex process gives value to that resource.
This is the gold standard to which the other 3 should be brought.
The leather resources right now respects 2 of those points. It has a processing facility (tanning tube) and requires time. Problem is that there is no resource involved in the actual refining. You just put your hides inside the tubes and wait.
Now, the actual real process of tanning is not something that we want so see implemented, this is a game not a simulation. At the same time though, since the actual process requires tanning agents, we can make use of it as a resource. In particular, since as a tanning agent you can use pretty much anything from leaves, to barks, to minerals, to chemical products, I propose that you put up to 8 hides inside a tanning tube just like we do now. Those hides depending on the number and the tier (tanning a troll leather is harder than tanning a deer) fill a gauge that is the required amount of tanning agents. Just like we have a required temperature for smelting, except that it depends on both type and quantity. As a tanning agent you can put up to 4 items inside. These should be logs of wood. The higher the tier of the wood used, the higher the value as a tanning agent.
After you have reached the required amount of tanning agents you can start the tanning process and 16 hours later whatever hides you have put inside are now tanned. This means that in those 16 hours you can tan a lot of low tier leather, or a few high tier ones with the same amount of tanning agent. You spend more in time but less in "fuel" or the other way around. Choices are always a good thing to have. Optionally we could also allow stone inside as a tanning agent, so that we give a meaning to stone in late game. It contains minerals.
In short, the better tanning agents you put inside and the more and the better the leather that you can tan at the same time. Right now rare woods are used only for a few crafts, and there isn't much trading of those. This would increase the value of locations close to rare woods (earthwood and deserts), and increase the trading of wood.
Wood respects none of the points of our golden standard. You cut down the tree, saw it into a plank and craft your bow. Like this, the wood plank resource will never hold a real value. At the very least, the wood must dry before being used. Now, this can be done by air, but for our purposes I think that borrowing the concept of wood drying kilns would be best. The process would be simple. Put wood inside, add some kind of fuel like charcoal or coal, wait some time, retrieve dry wood which can now be cut into planks. Technically you could use even other wood as fuel.
We would use a process very similar to the forging one. The only difference would be that since we can't exacly say "Higher tier, higher temperature" because it would be absurd to put Yew wood at 2000 degrees, we go with a concept of "Higher tier wood requires more time to dry" and so you need to put more fuel inside.
Cloth production respects no part of the gold standard. Kill the spider, craft the item, the end. Again, cloth products will hardly get a real value this way. Again, we need some process to prepare the resource, which requires areas, time and other resources.
In this case, what is usually common to all fibers before being able to spin them, is the cleaning process. Since we already have the tanning tubes for leather, and leather and cloth tend to be considered a single processing area, we could use the tubes also for cloth cleaning. It then would work in the exact same way as the tanning process I proposed, except that instead of tanning agents you put cleaning agents (soap). More fibers and of higher tier at the same time would require more cleaning agents.
Now the most obvious source ingame of soap right now is obviously animal fat, but we could make it obtainable from all those edible plants out there (oils), so that we give them more of a reason to exist. Lately, we could add a research to the tech tree under the herbalism branch, to make high power cleaning agents from reagents.
Using the previously proposed methods, we could give more value to all those resources while adding just a few facilities to the game and reusing the "smelting" process for all of them with small variations. Put material in the facility, depending on the material you get a required heat/tanning/cleaning/drying level, put the "fuel" and start.
@spoletta Not bad, some notes:
As Cloth generally makes lighter armor, it is okay that it has a few less steps than say metal. Cloth is easier to work with.
Also, Leather has 1 more step you didn't put in your list, and although it is minor, it deserves to be mentioned. You do have to put the hide on a Beam to turn it from animal hide into 'raw' leather.
I can definitely agree with adding a step between 'green wood' and wood ready for use. A drying station would work, as would a wood kiln. If you do want to add one more step to cloth and leather, that step could in fact be the curing/dying stage.