My comment in regards to Coff's was with transit routes, not class E airspace. I don't have plates for Coffs at hand, but if its similar to Cairns, 5000ft above the aerodrome does conflict with instrument approaches which do fly overhead (VOR/NDB).
Class E airspace does not protect the IFR aircraft coming into and out of aerodromes, as you have pointed out VFR do not require a clearance and could be in clear conflict without the IFR aircraft or Controller knowing anything about where they are, who they are and what they plan on doing. How many mid air's have happened in the US between RPT jets and light VFR traffic in Class E airspace? I can think of at least 2 without doing research.
If a pilot is deemed safe to fly a route such as along the Coffs coast line and remain clear of arriving and departing aircraft, then why not just give them a CTA endorsement and loop the other parties in on his flight (i.e. the IFR and ATC).
At the end of the day, CASA's focus is the safety of the traveling public. Class E doesn't support it.