The spell is not overpowered, because a CREATIVE DM would be able to find ways to challenge players who use it, even on a regular basis.
That's pretty much an admission of defeat when it comes to discussions of power level. I could come up with a level 1 spell that provided immunity to bludgeoning, slashing and piercing damage. A creative DM can find ways around it, which means it's not OP, right? Once you're talking about people running surveillance operatons on the PC's with Scrying or every group of monsters having Dispel Magic on hand or infestations of burrowing / incorporeal monsters everywhere, that's too specific. If you're going that far to rein the spell in, just admit it's busted and apply an actual nerf. It's not a dirty word.
My own precision nerf is to say it provides concealment and protection against natural weather, but doesn't provide a superior Wall of Force + Greater Invisibility dragon-proof bunker.