Whether you use an en dash or an em dash is completely a matter of style.
Indeed - the Daily Telegraph in London, where I spend much of my time as a freelance sub-editor (copy-editor to leftpondians), goes for en dash dashes, the Times of London insists on em dashes (which to me look far too long, but I’m merely a humble footsoldier in the Murdochian army). As it happens, I find pairs of dashes are almost always better replaced by brackets, or even commas ...
The Times. incidentally, has had a thing about being economical with the hyphens for, to my knowledge, the past 20 or more years - I quote from the current edition of its style guide:
Hyphens: generally be sparing with hyphens and run together words where the sense suggests and where they look familiar and right; eg, blacklist, businessman, goldmine, knockout, intercontinental, motorcycle, takeover, and walkover. Unusual hyphenations will be listed separately in this Style Guide. However, a few guidelines can be specified:
Usually run together prefixes except where the last letter of the prefix is the same as the first letter of the word to which it attaches: prearrange, postwar, prewar, nonconformist; but pre-empt, co-ordinate, co-operate, re-establish.
Hyphenate generally in composites where the same two letters come together, eg, film-makers, but an exception should be made for double r in the middle: override, overrule (not over-ride etc), and note granddaughter and goddaughter.
Generally do not use dangling hyphens - say full and part-time employment etc; but this does not apply to prefixes - pre- or post-match drinks.
for hyphenation when qualifying adjectives. See adverbs.
Always use a hyphen rather than a slash (/) in dates etc - 1982-83 (not 1982/83)
Note the hyphen, rather than the dash, in the year range, incidentally - Rightpond usage is, to my knowledge, universally to use hyphens in ranges ...
Trivia - in the days of hot metal typesetting (which I can just remember), to avoid confusion between the similar sounding en and em, en spaces were referred to as “nut” and em spaces as “mutton”, so that a copy-setting instruction might be, for example, “single column, nut each side”, meaning the type should be set narrow enough that an en’s worth of white space would appear between type and column rules.
edited to comment on Dave’s last post
As I’ve said elsewhere, the Times‘s typesetting software won’t show more than one space in output copy, no matter how many spaces you put in on screen, just to counter the “typing school double spaces"problem - the newspaper also redesigned its 1 (figure one) and 0 (zero) to look more like lower-case l and capital O, thus stopping all those people who learnt to type on typewritens which didn’t have one and zero characters and you had to use the lower-case l and capital O instead from typing lOO for 100, which, if no one spots it, looks hideous on the printed page.