This. Your SC are probably best saved for buying unit slots for now. When deciding whether or not to perform Premium Summons I prefer to base my decision on the Platinum and Gold units being featured rather than the Black units since you're far more likely to get those units. If I had your team the only current Plats I'd probably give consideration would be the following:
1. Uzume. Rune of Conflagration is pretty gonzo.
2. Gellius. Dude is a beast. I put him below Uzume because you've already got Olivie and Bernice so you should be good for a while. Still, if you ever manage to Awaken him and Bernice you'll have a very solid pure tanking core.
3. Thetis. A distant third since she's a niche unit you wouldn't prioritize for quite a while. Her stats are alright but mostly I mention her because she ignores status effects like paralysis post Awakening.
There's also a few bonus drop/gold get units like Monica, Cellia and Lyla that I wouldn't necessarily target but still influence my decision about whether or not to burn some of my precious free crystals. For example, I burned a bunch of SC last December because Monica, Lyla and Gellius were under the spotlight simultaneously.