Hi Dan,
You can compensate to some extent for the remaining variation of boost with Q, by adding a constant term to the volume control -- this is a small "zero compensation" that adds more gain at high Q (that is, near zero values of 1/Q), but has little effect when Q is lower and 1/Q is higher. To do this, add the blocks circled below to your filter circuit and adjust the DC source to minimize any drop in boost at (for example) Q = 20.
I'm not sure what's causing the asymmetrical response shapes. Try the state-variable filter by itself to see if it's the source.
Best regards,
Bob