You could add dangerous areas away from the elevator with some rarer resources to have a reason to go there perhaps. Maybe you could try other actions apart from hitting, like researching (having a creature/plant in an area for certain amount of time) or simply feeding or growing things to harvest later? Have creatures/plants that hunt other creatures/plants. Maybe try some environmental puzzles, like mazes, deep floors set in total darkness or floors with weird movement modificators, floors with traces of lost civilizations with still functioning tech and traps. You could try some interconnectivity, having blockers in the first floors that could be destroyed only with high-end items from deep floors or doors on deeper floors, which are opened with items found at the beginning behind some obstacles.

World's your oyster with this one :D