I actually just decided to abandon that attempt and regenerate the Rigify rig with the pelvic helper bones removed, as they're getting in the way of weight painting. I think I'll restart from the toes again, because there's a bending problem there that might require some extra edge loops. No biggie, I'm effectively learning (or relearning) weight painting while at the same time testing the appropriate construction of my mesh, so I never expected it go smoothly from beginning to end.

-- I'm not mad at you, just Westphalian.