Again, the reason the second revision works is that the words before the colon stand by themselves as an independent clause. Dashes can act as semi-colons, connecting independent clauses. They can take the place of colons in introducing lists. They can serve to insert an example, and allow you gracefully to get back to the main sentence. In Coriolanus , Sicinius and Brutus are the tribunes of the people-the voice of the people.
Any word processor can produce a dash.
However you produce it, don't put spaces on either side of the dash. Dashes often come in pairs. If you want to signal an interruption in a grammatical structure with a dash, you've got to keep track of the grammatical structure, and signal the return to the main structure with a second dash. Somewhat like colons, dashes are flexible enough to let you play with word order to create interesting sentences. Punctuation follows parentheses without a space.