There should be some sort of change so that challenge is the key to finishing with a high score instead of luck. As it stand right now a player with 10 mil score could easily get below a 600 score and players on day 2 and 3 can easily get 700+ scores because score isn't based on how well you fight or even strategize...it's about how lucky you get in the Destiny squares with receiving extra moves instead of losing moves.

I don't think that once unlocked, the extra bosses should remain unlocked but I do believe some sort of change needs to come so that fighting power and prowess makes more of a difference than blind luck.