I've always managed to keep my Spell Fragments and Combining Catalysts roughly in balance, but I appreciate that there are some (e.g. those with lots of Moonstone Libraries) for which this is not realistic. I liked Inno's solution to complaints over excess Spell Fragments (which was essentially to allow them to be converted into CCs and VV at a very bad rate of exchange). That gives players such as
@Gargon667 something to use their excess SFs for, but without causing a significant gameplay imbalance.
Although many might question the need for it, I suppose that a reciprocal crafting recipe could be created to allow CCs to be converted back to SFs. I'd suggest a rate of several hundred SFs in exchange for 10 CCs to be equivalently bad.