I was just thinking why doesn't luck work similar to runics? How about having up to 5 levels of luck with each level having a range or minimum number of items, minimum intensity, minimum number of mods? Of course difficulty of the creature will have to play some role. So at least if you are at level 5 luck and are killing a high level mob you know you're going to get decent items, even if the mods don't match up like when crafting with runics. If this is too powerful then also reduce the number of drops, so at least the drops you do get match your luck and fame level of the creature.