I believe the actual QNH is an easy fix, there are a great number of automatic MET stations on the BOM website, surely ASA has access to this data, be it real time or at fixed times.
If in the case of Benalla, if the altitude V's plot in RADAR coverage keeps the aircraft in protected area's, you would be correct then, MSAW might not have saved the day, we could play this game all day, what about the PA31 or the B407 in North QLD.
Guess ADS-B will make this equation even better ( yes whilst still in line of sight with a ADS station ), but not perfect.
Perhaps another spin, what if the two crays super computers you were talking about earlier would only enable the flight planned departure aerodrome, enroute Grids and LSALTs then destination MSA/MVA and appoaches ?, would this be better than the broad brush ?