Ah! I'm just now realizing that even my short-lived Selle Anatomica saddle had more wear on the left, which is more pronounced because of the cut-out. (I noticed this after mindlessly looking at old pictures of my bike--does any one else do that?)

I'm also going to try dropping the saddle a bit more and see what happens. A rider in my club noticed a few months ago that it seemed like my saddle was too high--and I had been riding it like that for about 400 miles--so that could have been an issue too. I always used Sheldon Brown's method for determining saddle height--raising it too high intentionally and then dropping it incrementally until you no longer have to weave back and forth as you pedal--and have heard that this can result in a too-high saddle position.

And it's nice to know I'm in good company in the leg discrepancy club!