I'd like to be able to harvest Luminous Russula (glowing cave mushrooms) and apply it to the tip of an arrow, that way when I shoot it into a wall or enemy, it would provide a soft halo of green light for the surrounding area, giving me the opportunity to target my next mark in dimly lit dungeons. Also, the soft glow effect would serve as a "tracer round" for marksmen. Same would apply to lit, or fire enchanted arrows.
Edit: To me it never made sense that you enchanted individual arrows, would it not make more sense to enchant the quiver, so that it may pass the enchantment onto the arrows? Using the same amount of effort to enchant an arrow you use once as a sword you use throughout the game has always been silly to me.