It seems that the en-dash *can* be used in English in some cases: 'high-priority--high-pressure tasks' from http://en.wikipedia.org/wiki/Hyphen I see. But this is a --more or less-- contructed case where using an en-dash instead of a hyphen makes sense. I agree with this example, the en-dash clearifies things.
But for general purpose the hyphen is used and not the en-dash. And I think the typesetting system should be set up to fit the general purpose. (Hans has a different opinion, I know.) BTW: If the appearance of the hyphen is unsatisfying it is better to choose a different font (or hyphen from a different font) or maybe to »correct« the font instead of altering settings of the typesetting system.
Concerning the hyphen sign, '\setuphyphenmark[sign=normal]' works as expected on my system (= normal hyphen sign). But it was (is?) not usable because, in case of a line break, the hyphen sometimes was placed at the beginning of a new line. You're right. I mixed things up. My fault. It always produced the right sign. And the bug is fixed (Thanks Hans!). So you can use
\setuphyphenmark[sign=normal] again in your cont-sys.tex ;-)
With '\def\compoundhyphen{-}' the compound hyphen breaks correctly. Not needed any more.
Marco