Disable non-breaking space (Option-Space) specifically in Xcode
I have found a somehow dirty workaround to disable the key combination for Xcode only:

To disable alt/optspace add a new keybinding in the file  IDETextKeyBindingSet.plist in the folder /Applications/Xcode.app/Contents/Frameworks/IDEKit.framework/Resources.

Open the plist and add a new dictionary called 'Customized'.
Create a new child named 'Insert No Alt-Space' with type 'String' and the value 'InsertSpace:'. Save the file.

Open Xcode -> Preferences -> Key Bindings -> Customized
Highlight 'Insert No Alt-Space' -> Key and enter alt/optspace.

In the future you will get an audible error message typing the combination but nothing will be written.

Until now i haven't found a method to just insert a space instead of a non-breaking space.

Probably you have to redo the modification with every new Xcode version.