I think having a "big" enemy or named one at the end of every cave is a bad idea , some caves are just empty , sure it's annoying going into a cave and exploring and there is nothing there but an event or "leader" at the end of EVERY cave is just terrible , it would just be repetitive and make the game monotonous , but i do know where the point comes from , in oblivion most caves were unimportant and just a waste of time but i think instead of a boss fight or a variation of it isn't needed to make them useful , having some caves be a shortcut through a valley or have some open caves , like on a strand by a river , enter the big hole in the cliff face instead of the obligatory wooden door oblivion had on everycave that made it look like a lower class hobbit hole
, some caves should have BIG entrances to make it more immersive and instead of having "trash" caves, some diaries of lost explorers could be found in there , some dark and some just straight up funny
, not really a quest really , just stuff put in for fun and to show that other poeple in the world other than you explore , and sometimes caves are just empty adds to the game world
so in short , caves dont have to have big battles at the end , there can be other variations
1. caves as passageways
2. caves as areas for dark of funny diaries like ironic deaths or like the adventures of herbert daring dashworth in fallout 3 , that was so funny
3. have some caves big and open ( by open i mean liek open cities) and less of a hobbit hole look , more like this --> http://www.jillbert.com/gallery/caracol/Rio_Frio_Cave_opening