OH right adding onto super boss replays idea, you could give rewards for beating them in X turns. or drawing the fight out for x turns too. i would think something like:
beat X boss within 10 turns = 2 power stones
beat X boss within 5 turns = 5 power stones
draw out boss fight to 20 turns = 5 fortune stones
draw out boss fight to 30 turns = 10 fortune stone
probably best left at one time rewards... but maybe you could let us farm 1 power stone per within 5 turn victories after the initial win or something?