Originally Posted by hypo

But the special stage is not valid for the daily "5 expert-level pests", so if you do at least 3x 1-4 levels, you gain 40 bags (100 - 3x20)

Correct (I actually always do all the event dailies, even the one for the beginner difficulty), but for those with some stamina to spare after doing the event dailies, the Special Stage is the most efficient and quickest place to do it.