I didn't really used an AC on the main part of the game. You don't really need one. The most important item is the miror of truth lvl 9 (remove normal monsters, so you only need to kill the boss to clear a stage), and thus, if you OS them, it's pretty quick to get lots and lots of stones (I did around 15 meaningful rebirths, with the last ones at 10K stones).

However, for the girls minigame, AC is a huge advantage.