Pretentious? Come on. There’s nothing inherently wrong with spacing your em dashes. It’s even part of the AP style guide.

I personally wrap them in thin spaces (U+2009), except in fixed‐width fonts, where I use an en dash with full spaces instead.

The AP is a poor source for a typographic style guide. They are a wire service not professional typographers, and my speculation is that their conventions come from a context of typewriter manuscripts rather than properly typeset books. They eschew en dashes and use hyphens to indicate ranges (e.g. 10-20 instead of 10–20) – something no professional typographer would condone – because they are expecting someone with a typewriter to only be able to type hyphens, whereupon the choice is either one hyphen or two. So in a manuscript you get spaces around pairs of hyphens -- like so -- standing in for dashes. Their style guide is designed so that someone doing the newspaper typesetting can directly copy the typewritten manuscript over to the press without thinking about what kind of dash to use.

In fixed-width fonts, do you literally use an en dash (U+2013) or do you use hyphen-minus (U+002D)?

I use UTF‐8 except when I have reason to stick to ASCII. (One such situation is public mailing lists, where people’s misconfigured mail clients constantly butcher any non‐ASCII characters when replying.)

No editor is going to tell you not to do something that lots of people do. As the other reply says, you're being a tad pretentious over nothing much. Chill.

In professionally typeset material people use either spaced en dashes – like this – or un-spaced em dashes—like this—but spaced em dashes are unconventional and unprofessional, frowned upon by anyone who knows what they’re doing. Sometimes professionals put hair spaces or thin spaces around em dashes — like this — but on the web those often are rendered improperly, such as on this forum. Try copy/pasting this paragraph into a rich text editor and swapping between a few typefaces to see what the effect should look like.