I honestly couldn't think of another skill I wanted, but thanks to that gold I was able to finally bring Aqua up to 120/CC4 and let her stand beside Okyuu like she deserves to. Plus given how the toughness ability works she'll definitely make great use of it, and she even has five blocks now which really takes advantage of some of her bonuses.
If they do run another TD collab for halloween then hopefully I'll get the chance to finish awakening her, she really has turned out to be far stronger than I expected her to be and it makes me glad that she and Okyuu team up together so well.

I still think her weapon just being a giant crab that happens to ride around on her head is pretty funny too though.