The event is only made for "maybe" getting 1 Item(Bow) or 1 Maiden.

With over 4 Days left i think it's possible to get 700 arrows depending on the drop amount. What i've seen is, that on Lv12 the drop is 1-4 (maybe 5 max) so if i get every run ~2 arrows = 350 runs = 2100 Energy (i have 149 arrows atm)

Every day you can get arround 240 energy (without any refill or level ups and sleep time) so with 4 days you will have arround 960 Energy...

I think events like this are only made for ppl forcing to spend some gems, but i can not say anything bad about it, because on the halfway of the event everyone got 500 gems.
I also want to keep this gems, but i think i need to spend them if my arrow dropluck is low.