The problem with that is, on Nutaku "rate up" basically does nothing for Jewels. I thus wouldn't really recommend this.The problem with this is, Dark Amaterasu is unlikely to never ever be available with Jewels again. Osiris as well, though it's not impossible.Well, you can only do two things with Jewels:
1. Expand your inventories
2. Get new Hime from Gacha
If you don't need more inventory space... go for it?