That's probably not worthless, if you have a type cute chibi, equip her with the best items since they get boost for current event. You need to set it in the event specific chibi tab. When it comes to event, fully equipped chibi can help about as much as a a 20 cost idol so you technically get like 23 slots (10 front, 10 back and 3 chibis). But unless you have items for all of them they are worthless. So using the chibi gatcha is pretty good, thats all I use the puchi money on since I already got the girls I wanted (I even got Rika twice, one I bought her and once I got her S-rare from the 10% S-rare so it gave me the scout medals and also her signature lion clothes).
But to be honest I don't really care that much about the chibis, often even forget to send them on a lesson xD I just use them for the events so I have that auto setup for best event appeal.
But for the regular setup I tend to my girls a lot, everyone lv 70 and MAX affection, lvl 10 feats on the important buffs like passion maximum attack, since my front members are all passion 16+ cost S rares.
And mainly I come and check on them often to see the full version picture since the art is so damn good xD When I compare it to something like kancolle where the art is half of the time really bad and the other half is just acceptable, here I even love some of the girls I would have normally never liked (big boobed etc) because they have just so damn cute art.
I hope I get the current event Miyuki S rare (otherwise I'll have to buy her xD), its so cute too. Its called "Cute Cook" but to me it looks more like "Miyuki Yanase, the knight of the gurb and protector of the well fed" or something xD some epic loot, Pot Lid Buckler rare shield and Sweetblade +1 legendary shortsword xD

I knew you could do the puchi clothing gacha (aka the biggest waste of virtual cash I've ever seen- yet I still keep playing it and I'm invariably shocked when I get another copy of Rin's dress or a common accessory)
I don't think there is any other use for that currency though, except the new chibi for 1 million xD So not really a waste, more like regular conversion

But yeah I have tons of copies of the same looking rarity 1 clothes lying around and I don't think you can even throw them away xD And that's only after like 2 months of playing...
(oh nvm, I just checked and you can sell them for about 100 each, 1000 for rarity 2 and 15000 for rarity 3)