Actually, some of the levels were redesigned during development, and a few opponents left outside the new level boundaries. The battlefields are randomly generated, though, so areas or opponents cut off are problems with that.
I never worried about luck; more is better, but I never went out of my way to get or keep that bonus on equipment, etc. AFAIK nobody has provided any detailed feedback on how it effects loot... Actually, I don't remember anyone giving any general observations over a long period or repeated playthoughs, either.