I like the idea of more spots to harvest materials for barkskin potions. Currently, there's 1 area to get the dread treant saps and its usually farmed out. On the other hand, these potions can be bought in limitless supply from at least 2 NPC's that I know of, so there's not really that much of a -need- for more drops or gatherable resources.
However, if it were changed so that the materials to make the barkskin potions were made more readily available, I would be in favor of removing them from the NPC vendors. I think of these potions as both a necessity and also as sort of a "magicky" item, and while I think most vendors shouldn't have them, I also feel like they are needed for tackling dungeons.
What I think would be a good idea is to make it so that "Tree Sap" chunks occur randomly when you go out and cut down the already craftable trees. This would make it so that the materials would be a frequent enough drop to make it so that crafting the potions yourself is a viable option, and also woodworkers could get some extra income by selling the tree sap chunks if they didn't want to pursue herbalism.