You have to earn the voices by buying the events again, so you'll need to burn them at some point.
That said, they're decent CE EXP cards, and you should save five for the initial boost to event currency.
The grind is brutality. At max, you can only get 700,700 chocos per run. Just getting from 30M to 60M to 100% the event takes 49 runs. If you already aren't burned out from lottery farming back during Christmas and Da Vinci, you will be. If you're going for 100%.
In Challenge Quest news, Hokusai is unfortunately not ideal, so I had to run Meltryllis and Okita. Ugh enemy triple crits, though.