I have had 7 corns in the first 7 tiles, so average of 1 per tile. Not a bad haul. Did the math by the way, if you are capable of clearing all 40 missions then you only need 21k feathers to complete the event and buy the third copy from the shop. With the average of corns being say 5 per full run of 40 missions (and it seems to be more then that for most people) you will have 35 by the end of the event without spending a core.
All in all i'd say this is not a terrible event. Especially seeing that the mission levels start at Commander level -10 and seem to end at commander level +4 or +5.
Flower Knight Girl: 255445855