considering i'm packing 19 of the 6* girls in the game, i'm burning through coins faster than I burn through stamina...
i tend to find myself spamming flower gems at stam refills a ton just to get the coins... especially since I'm almost never doing the flower gem gacha anyway (unless they have a good step up or something...)
if it wasn't for the 50% potions being added as well, i'd likely would have drained storyline of all it's flower gems by now (i got them all up to chapter 24 though)
they are EXPENSIVE to build up, especially the Bloomable ones... but my god does it feel worth it when you get them to lv70/80 (and maxed out on ampy increases like my Lycoris)