I always try to keep 1,000 (free) rubies on hand for events that either require an investment or where you can clearly gain something extra. This event was no exception - I immediately unlocked two extra slots, and I have already cleared two of the prizes, so that was probably overkill. On the other hand, there's zero stress involved now. I was pretty sure I'd have to unlock at least one extra slot when I saw that the event was only for a week. That's less time than we're usually given.