Moreover, there's very few things a spellcaster wants to stand next to. Another caster being one of them, but also among the least likely in an actual combat situation.
The hemisphere of "I won't die this turn" has more serious potential, although I'd still consider it far from broken. Unlike Wings of Cover, it will block your line of effect AND your movement for rounds. A hemisphere 'centered on you' will of necessity enclose you on all sides except down, as long as you're standing on the ground. Good spell when you're already airborne, but then it only protects you from one direction. I can see a lot of situations where this spell would be handy to have - but I also have a hard time figuring out anything non-defensive about this spell.
In the best situation, the enemy will waste a powerful attack of some sort on you, then turn to your allies, while you are (due to being airborne) not constrained by the hemisphere staying in place. You just traded a 4th level spell slot for whatever the enemy was throwing at you, which might be worth it at higher levels. In the worst situation, you'll be caught off guard by something and have no other resort but cast this spell, standing around in a jar for all to see many rounds thereafter while the opposition kills your teammates.