It depends on what you are fighting. In general I agree that once you get to level 10 you atend to be in areas where mod fortification or higher gains the advantage over invulnerability.
I personally use the robe as a clicky. Even at level 19, I still occassionally use the invulnerability when fighting a mob that doesn't do a lot of damage per hit. But I carry and click to DeathBlock of Greater XXXX Resistance all the time. One of the advantages of robes is that they can change quickly.