I redid all the speaker bolts this morning. To my surprise – it had been a couple of years since I last checked them – all but two or three were fully snug before I backed them off to apply the correct torque.
Expectation bias notwithstanding, the speakers sounded exceptionally good when I listened to Thelonious Alone in San Francisco a little while later, most noticeably in the way they seemed to disappear while the music filled the room (and my copy of that record is a nondescript 1980s reissue). Whatever about specific torque values, I’m convinced there’s merit in getting all bolts of the same size in a given location done up to the same value. I shouldn’t leave it so long next time.
Per the advice here, I reduced the torque on the screwdriver to the lowest setting before putting it away.