You can cast ethereal almost anywhere

Don't have to be limited to casting it outside a dungeon. If so, it'd be totally broken.
Tip 101 - Sacrificing a summoned pet to buy time.
If you find yourself in a situation where you have been aggro'd and can't cast ethereal, first summon up a pet. Pixie or imps works best since those spells are fast. "All follow me" then invis/hide to break any aggro. Depending where the mobs are, move 1 step away so that your summon is between you and the mob.
edit: For clarification, issuing the "All follow me" is to prevent the summon from running about and trying to engage any aggressors. You want it to stay put to act as bait while you move into a better tactical position. You also want to keep it alive longer so that they act better as bait.
Now cast ethereal voyage in peace. Should the mob go aggro, it will target your summon first.
5th level circle = 5 pixies in one summon. So as long as they are not subjected to area damage, even if the first is killed, there's 4 more to go. More than enough time to cast ethereal voyage.
Did I also mention that I'm very sneaky?