2. The "area frequencies" are primarily for aircraft in class A/C airspace.
This is incorrect, if by "Area" you mean FIA - Flight Information Area frequencies.
AIP:
Flight Information Area (FIA): An airspace of defined dimensions, excluding controlled airspace, within which flight information and SAR alerting services are provided by an ATS unit.
The FIA frequency is the appropriate one to use when stooging along in Class G (away from the vicinity of aerodromes where a discrete CTAF, or 126.7 are used of course).
In fact in the event of having strife, a broadcast by you on an FIA is more likely to be heard by ATC and/or other aircraft, than relying on other aircraft hearing and understanding you on 126.7 (and them then being put in the position of trying to figure out who to notify and on what frequency …….).
The fact is though that Airservices will only publish NOTAMs for certified and registered aerodromes.
No, the others are covered by Brisbane or Melbourne FIR NOTAMs. Organisers of fly-ins, field days etc. contact their local CASA Operations office and they have the NOTAM issued by Airservices.