Mostly I mean the idea of adventuring in an enclosed environment with few ways to alter or change this on the cheap.still don't think you do. Dungeons are not much more than a specific type of setting. This would be akin to saying city adventures, or wilderness adventures.
But then again, I'm pretty clueless as to what you mean by "level 30 equivalent stuff". Do you mean party abilities? magic items? NPCs? I just don't see the need for any of that.
Level 30 stuff would have effects that make Tier 4 stuff costly, inefficient, or not as versatile again.