Not a bad idea at all to vary the caps. I'd make the steps approx an octave apart. 6n8 is where it is now, perhaps add 15n (one octave down) and 33n (two octaves down), and try 3n3 (one octave up).
I wouldn't switch it though. For the cost of the switch, you might as well build multiple parallel VCF circuits, and mix the outputs. That allows for the possibility of running more than one bandpass at the same time, which can sound really nice. You'd need to match the FETs so they track together.