OK, I figured an update is in order. I've recently swapped out 2 things in my speakers, the Sonicaps to ClarityCap MR's and the 1Mh Erse coil to a Jantzen 1mH wax foil coil.
Results? The caps are still burning in, but so far it's been a step sideways as far as I can tell at this point. Disappointing (so far).
The Jantzens, on the other hand, are the real deal. An immediate (and big) improvement over the Erse perfect lay coils I had in there before. Specifically with high frequency clarity, imaging, clarity between an initial note strike and it's reverb (this was muddier before, particularly with things like pianos, cymbals, triangles, etc). Overall it just allows the creation of a more realistic space, and the instruments sound more realistic within that better defined space.
I'm shocked. Honestly this is the reverse of what I expected. I expected the caps to have a big impact and the coils to have a small change. But it's the opposite.