Will do. That idea made me go read more about bypass caps, too---thanks for the motivation. I knew they increased the output of a stage by reducing/eliminating negative feedback at the cathode/source/emitter, but for some reason I never put it together that that less negative feedback at the source = more input gain within the same stage, and more NFB = lower gain in that stage... cool.
you could try replacing r1 and r2 with 33k each, with a 100k trimpot between them connected to r3/c3. then you could shift the bias point of the mosfet while watching the cro to get the maximum swing from your particular device. I'm surprised this hasn't already been suggested.