4greens first point I suspect derives from the standard for independent parallel instument approaches. If the centreline spacing is between 1035 and 1525m, PRM (or similar) must be used. If the spacing is greater than 1525m, standard radar is sufficient. At least that's my interpretation of the standard.
PRM pilot guide has some more info. The relocation point may have been confusion about duknweev's comment about relocating the PRM operator consoles to Melbourne.
IVA's can't be used (easily) if the cloud base isn't above the highest IAF.
PRM approaches will appear to pilots to increase delays (they generally add around 20 track miles in the circuit) but the airport will actually be landing 10 more per hour than would otherwise be accommodated. The systemwide delays are reduced significantly as SM4 pointed out.
As far as flying the approach, PRM will only normally be used between 7 and 9 am Mon-Fri. And that may happen on average just once per week. Your chances of copping an arrival during PRM ops are very small. Even the approach controllers would only do it a handful of times a year each.