Nit: since it's the main copy on the page, maybe worth using em dash.

En dash with spaces (which I have here) and em dash with no spaces are both generally considered correct in this context. I've also wanted to write an em dash with spaces in the past but I've rarely, if ever, found style guides that encourage it.

@spicyj sorry to randomly bikeshed my way into this discussion, but my experience was that the spaceless em was mostly advocated to me by designers that had done work in europe (since it's apparently a common newspaper pattern) whereas the en/space is more common here (and among my mostly american faculty for whatever reason). follow your heart, ben (although i also put a vote in for the hard em dash without spaces since i always feel it adds an air of immediacy in the break 😸 ).

I'm not an expert on this. I thought en dashes are mostly reserved for number ranges:

http://english.stackexchange.com/a/2126
http://www.thepunctuationguide.com/en-dash.html
http://www.chicagomanualofstyle.org/qanda/data/faq/topics/HyphensEnDashesEmDashes/faq0002.html

I haven't found a result recommending en dash to be used to delimit a sentence yet. On the contrary, all the manuals I found so far recommend em dash for this.

The only difference is they mostly recommend using em dash without spaces. I agree this looks a bit pretentious on the web, and this seems to confirm it's fine to surround em with spaces:

Most newspapers — and all that follow AP style — insert a space before and after the em dash.

Where can I read about using en dash instead of em in this context? Maybe this is some newer usage I'm not familiar with?

one "authority" (which agrees with alpert in this case) is robert bringhurst's elements of typographic style. my v3.0 copy says

5.2.1 Use spaced en dashes – rather than close-set em dashes or spaced hyphens – to set off phrases.

I'm not much of a prescriptivist, sadly, i just like the look of the close-set em dashes (especially if the em dash in the font doesn't include any sidebearing space around the glyph). i'm definitely of the school of thought that it's good to explore any arguments for/against and then make whatever decision you think works best in this sort of case (if you've commissioned a typeface for close setting em dashes (or even if you haven't), i think you should be allowed to use them however you like, like wearing sneakers with a suit, which some people consider untoward and others perceive as a mark of a kind of fashion).

@gaearon The Stack Exchange link you used also mentions " – " as the last bullet point for en dashes and the Wikipedia page it links to uses the same construction multiple times in its prose.

I'm just happy someone cares about using em dashes 😊