Controlpoints of hidden objects can still be selected and manipulated:
Related to this is the possiblility of transforming Hidden objects when grouped with a visible object:
I’m not sure what a best solution would be, but I think at least the fact that hidden geometry is ‘selected as well’ should be reflected in some way. I noticed that in the last example, if I scale with the Gumball handle I get a grey preview of the hidden curve:
How about permanently showing this greyed out geometry whenever hidden geometry is selected?