Regarding special locations and general accessibility of items. Maybe the size of the overworld could be used for that.
Right now outside of specific points of interests there's little reason to travel anywhere since all resources are accessible near home. Would be interesting if some, the less basic of them would be nearly impossible to acquire in the wild aside from occasional resource node once in a blue moon (together with loot drop adjustments as skellies certainly drop too much rubber, oil and electronics for how primitive they appear to be, living in ruins and whatnot and stone protrusions seem to be 50% made out of pure metal at times) with some areas all over the world where those defendable oil rigs, metal wrecks etc could be found.