Outsmarting the Smart Dash
All that to say, it’s unfortunate that you can’t separately turn on/off smart dashes and quotes in System Preferences. Fortunately, though, you still can through Terminal with:
defaults write 'Apple Global Domain' NSAutomaticDashSubstitutionEnabled 0
Update (2016-04-25): Rosyna Keller notes that it’s best to avoid “Apple Global Domain”:
defaults write -g NSAutomaticDashSubstitutionEnabled 0