sup. a big fan of KotC1 here.
One thing to spice the game up would be to introduce optional dungeons/encounters that are not intended to be easily beaten by a regular(even a final boss ready) party. Maybe some obscure multi-floor dungeon thats only mentioned in few npc conversations that would take some effort to find. Where even the first-floor would offer the challenge(and rewards) of the greater difficulty than a final boss encounter. Perhaps to offset the difficulty differences, once you clear the entire place, there would be a trigger that would change the final-boss encounter accordingly(giving him additional powers/allies).