Good news is that I did end up finding the crystals in the Burning Steppes. And quite some bit of Alliance farming them (are you stacking oils for Naxxramas?).
Luckily most of them focused on the scourge and not on me. As described in a bugreport, I did not see any necropolis flying in the sky. All scourge creatures are missing their money loot. Killing scourge creatures does lead to flying spells hitting the crystal (which cannot be selected... but probably should) but it also keeps me in combat because reasons.
|90% of what happens during this invasion|
Scourge minions melee hit me for roughly 70/hit (reduced), which would mean 88/hit or so unreduced, which looks too low. Doesn't seem to be much for me with this event unfortunately... maybe I will farm some for reputation until revered (that'd mean less arcane crystals to buy).
|Unfair world, mages can kill 50 or so of those in 20 seconds. Say hello to vanilla.|
... On a 100% unrelated note my roughly 2 years old report about Gahz'ranka's slam hitting for roughly 10x too much damage is now #confirmed, yey!