slothen: In general, I agree. Some comments:
The bigger answer is to move away from having a single template for skin and bone. This would be some work, but wouldn't be very complicated and can all be done in the raws. We could make elephant skin inherently tougher by using a different skin template.
Yeah, although I think relative thickness is part of the problem. The relative thickness of skin tends to be the bare minimum, which is probably too thin even for humans, never mind something like an elephant. Apparently, according to Wikipedia, most human skins is 2-3mm thick. In DF, this would imply that without being particular fat or muscular or anything (just going by relative thicknesses here in b_detail_plan_default), someone's arm is 110-165mm thick, and that's just to the center, so the whole thing would be 220-330mm straight through. That's 8.7-13 inches. Clearly, an arm isn't actually that thick, so presumably skin in DF is thinner than 2-3mm. This effect is even worse for thinner/smaller parts like hands and fingers and toes, where the skin is (probably) at least as thick as on other parts in real life, but on DF still has the same relative thickness compared to other tissues. In real life, a finger doesn't have skin that's 1/5 as thick just because the body part is 1/5 as thick, but in DF that appears to be the case.
This is true for a lot of relative tissue thickness values. Like I mentioned, the head in DF has a layer of fat and muscle comparable to other parts, which is just silly; people might get fat faces, but they sure don't get fat, muscular craniums.
Another example would be bird bones, which are outliers among other vertebrates for their low density, so all flying birds (not penguins see) could use a bird-bone template. The other benefit to this is suddenly there will be a functional differentiation between hoary marmot leather armor and elephant leather armor.
I agree. However, with leather, I think the thickness of the material should also probably matter in addition to the material properties. This would require some reworking of how items are defined, though.
Now to point 8:
Actually I would argue that in the limitation of how Dwarf Fortress simulates things... Silver would make an Excellent Blunt weapon material. That is however because the game doesn't simulate the weapon taking damage as well. A Silver weapon would be rendered useless rather quickly.
That's not the only issue. A steel mace would generally be built at the appropriate size for a given creature, such that making it heavier would confer no benefit. After all, if a silver mace would do more damage (durability notwithstanding), why not just make the steel mace
larger instead? In realistic terms, the weapon would be built at the optimal mass for the creature holding it, regardless of material, such that using something super-dense like silver wouldn't be very beneficial, because they'd just make it smaller. If four pounds is the appropriate amount of mass for the head of a hammer, they'd make it four pounds, and making it out of silver instead of iron or bronze or steel would just be pointless.