My punctuation questions provoked good comments, including a grammar correction from Meg (which created the opportunity for a [third {level of} parenthetical] comment) and two professional citations from Hannah:
Per Strunk and White, third edition, Elementary Rules of Usage #8: Use a dash to set off an abrupt break or interruption, and to announce a long appositive or summary.
A dash is a mark of separation stronger than a comma, less formal than a colon, and more relaxed than parentheses. . . . Use a dash only when a more common mark of punctuation seems inadequate.
I complained that the S&W doesn’t seem to distinguish between varieties of dashes, and Hannah had to invoke authority:
You’re just begging for me to drag out Chicago, aren’t you? Seriously, man, dashes, en-, em-, or otherwise, have specific uses. En-dashes mostly replace the word “to” in a span of numbers or hyphen “in a compund adjective when one of its elements is an open compound . . .” (see CMS 15, 6.83-6.86). Em-dashes are used as S&W describe (see also CMS 15 6.87-94). Of course, when communicating with typesetters, proofreaders specify the type of dash required.
My only quibble now is wondering if “typesetter” is still the correct term, or should it be “typographer?” In either case, I guess rules are rules, which drives improvisers like me crazy. But if George Bush can be The Decider, then I guess the Chicago Manual of Style can be The Reference. And I can be Back To Work! Or at least, Back To Work.