To me, as a mechanic the Black/White Mana feels arbitrary and barebone, lackluster, whatever-you-want-to-call-it. It honestly just makes half the main-line spells feel like mere bloat.

I'd like the spells sourcing each to feel different and perhaps also for each to have its own uncombined output as an option, even if used more rarely and situationally than the current balanced expenditure (enchanted combo + follow-up). Then it might actually feel like it's doing something other than doubling up its spells into needless A|B pairs of which both halves function identically.