listening on 121.5 on approach is very important - it might be the only way that ATC can call you if you screw up a frequency change, or suffer an undetected radio failure.
Not really. There are well-established procedures in place for comms failures, and if you suffer one, ATC will automatically keep other traffic clear of you and give you priority. Same applies if you screw up a frequency change, although I can't imagine very many IFR aircraft these days don't have instant reversion to the previous frequency.
More to the point, if you can't manage to fly an approach safely with a bit of chatter on the radio, you shouldn't be flying IFR at all.
I have worked for 7 European airlines over a 20 year period, and not one of them included monitoring 121.5 as an SOP. There might be some point to it when traversing large areas of wilderness in Oz, but not in terminal areas.
I suppose if you happen to be flying an aircraft in a tense and dangerous part of the world, with warships on full battle alert nearby, there might be some point... but then, how many airliners have been destroyed in this way around Australia?
Why don't you just go around to the premises of the worst offender and settle it like men?
