I'm in favor of adding an enabled/disabled state to controls. 

It is a nice way to solve the GUI issue of how to gray-out / disable a control in a general way. The alternative is to define a separate control that reflects the enabled state (e.g. for every control like  [Channel1],filterLow we have a separate control  [Channel1],filterLow_enabled.
 
I think it's bothersome to have to add an additional connection to the separate enabled/disabled control in the skin definition. It would be cleaner if the skin definition only had to connect the control itself to a button / knob / slider widget and the widget listens for changes to the control enabled/disabled state.