...for an operation such as Angel Flight, is it possible to have some sort of mentor/Chief Pilot/Dispatcher/Co-pilot-by-telephone to validate a pilot's decision to depart into anything other than Day VMC?
I think this is a reasonable idea. However, CASA will not allow it. Years ago the aerobatic club used to have a coaching system. It worked really well. It was a mentoring system for guys who already were qualified, but benefited from coaching for competition aerobatics. It also provided a really nice support structure to provide some peer pressure in regard to general flying standards.
Nice idea? CASA prohibited it because the "coaches" were not qualified instructors.
In my experience doing Angel Flights, the AF dispatcher will not help with a decision except that they err on the side of not going if you are vacillating. I have found them to be hugely supportive if you decide not to fly.
Angel flight already have tougher qualification & currency requirements than many parachute or scenic flight ops. There is no evidence of problems with Angel Flight.
On the other hand, the Horsham accident showed flaws with CASA's licencing, the provision of forecasts and raised questions about the provision of air traffic services / flight following.
These are the issues that should get scrutiny - not "community flights".