I found out I'm very comfortable not parenting the two IKs at all, but moving them together by recalling them with a hotkey (ctrl + number from 0-9, then press the number to recall the selection).
Another potential nice thing I was afraid to do at first but then didn't regret is disabling the IK to use forward kinematics instead when needed during an animation, so that the IK would actually work only when needed, that is to say, when touching the ground, and still move nicely when a limb was up in the air instead.

Otherwise, I too used your setup, which I believe it's similar to Raptor and Spineboy example projects as well.

I found out parenting the foot directly to the IK target bone is also a neat thing because then the foot doesn't require its own IK target, but this depends on the style of the drawing, cause it tends to work really well on short feet or a flat art style mostly.