Originally Posted by Arekusu

If you have a girl at 100 and find her again in gacha you get a Wild equivalent to her rarity, which is a much better value.

Small correction on this. If you haven't unlocked EX levels, finding a maxed card in gacha will level a random card of the same rarity, or (very rarely) one of a higher rarity. If you have unlocked EX levels, a 100 lvl card will gain an EX level, or if the EX level is also at max, then you'll get the wild card of that rarity.