The default description of Greater Sanctuary clashes with how it actually works ingame, which often confuses the roleplay surrounding Greater Sanctuary users. So please ignore the description entirely.

An Amia the spell is considered, for RP purposes, to be a save-less version of the level 1 Cleric spell Sanctuary. You are not on (or partially on) the ethereal plane; what the spell does is penetrate any magical or inate supernatural barrier to mind-affects and makes all individuals incapable of choosing to hurt the caster directly. They can still be seen, smelt and heard, but direct hostile action is impossible.

Note that this does not allow you to escape from all roleplayed conflicts: for example city guards can still detain you by other means than physical assault. Locking the city gate, for example.

Furthermore, when in battle(in game mechanics terms, set to Hostile) the spell affects your senses too, making them incapable of detecting the caster unless they have the powerful magical senses of a dragon or Umber Hulk. Even if they have such eyes, they cannot choose to hurt the caster directly.

On an intellectual level, any semi-intelligent character with experience of mages will be able to deduce a GS'd caster is probably in the general area from in-character clues like the existence of summons, or from having seen them cast it in the first place, or from having a friend or summons with 'real' True Seeing, so using area-of-effect spells/feats in PvP is not considered cheating, provided the various purely out-of-character means of locating someone have not been used.

For example, if you have set a Weapon Master to Hostile during a roleplayed conflict and then cast Greater Sanctuary, you are legitimately vulnerable to Whirlwind Attack being spammed while you buff in 'safety.' The WM has 13 INT. He will know you are around somewhere, even if some part of his brain is ignoring the fact his eyes/ears/nose are telling him exactly where that is.

True, just that with all the nerfs it's getting I'm wondering what's the point of even having it now. It's great for running away, but...

Ever try not to run over an entire floor of traps stacked on top of each other like nobody's business? Kinda hard, if you couldn't pile 6 traps on top of each other in area transitions or doorways, maybe, otherwise you're screwed either way.