While when 3 donation contests are going, yeah it can be silly, but they can be good, because there will be a point where your harem is maxed out, nothing in the shop worth buying and unless there's a Pachinko contest, the normal Pachinko is kind of meh, but your cash continues to roll in. The expansion of the affection levels for some of the girls helps as the final ones cost quite a bit, but the donation contests can be useful as there will be a point where "What will I do with all this money?" comes up