Yup: I was missing something obvious. Or, perhaps more accurately, logical—once someone pointed it out to me on Adobe's "Photoshop Lightroom" forum website. (I'm sure this is documented somewhere, but I wasn't able to find it on my own.)
To see the parameters used for a past local adjustment: (1) click on that point in the develop history sequence, (2) select the appropriate local adjustment tool (e.g., brush), and (3) click on the anchor point for that adjustment in the image preview. The then-current settings of the sliders will then be displayed in the drop-down local adjustment panel.
