Safety isn't an issue if the recommended procedures are followed. Since we had a scare recently, we introduced a rigorous inspection regime, and have had no problems since.
Snooky is quite correct- the 757 has a long history of this, there was a diversion just a few months back with this problem. Contaminated cabin air can happen in ANY turbine-powered aircraft that uses bleed air from engines or APU for air conditioning.
If the Aussies issue an AD grounding the fleet- which I doubt they will- they will be consigning their operators to financial hell for a very long time- for no tangible benefit over current procedures. Better ground the 757s while they are at it, in fact why not ground all aircraft?
Better still, follow established engineering procedures, and the problem is not likely to recur!