"The fact of the matter is, is that this deterioration of traffic into Melbourne has really only been noticeable since early November. Likewise the use of single runways in CAVOK with light and variable winds."
April through October ish, the most common winds at YMML are North Westerlies, hence lots of 27/34 operations. November through March the most common winds are Southerlies/South Easterlies with the occasional strong Northerly, so much more use of 16a/27d and 16 only with the occasional 34 only day.
Rapid Exit Taxiway Golf has only been closed in the last couple of months, and has the biggest impact upon Southerly/South Easterly wind days. I suspect this is the single biggest reason you've noticed a deterioration of traffic into Melbourne. There have been no other significant changes to procedures or console staffing.
If there is any way we can use a Runway mode including 2 runways, we do. We do not select single runway modes to be obstructionist. There is a controller constantly monitoring the weather and looking for the opportunity to use a 2 runway mode to increase efficiency.
Le Pingoin is correct in that we do not quote tailwind/crosswind conditions for a non duty runway on the ATIS. My example of wind 120-180 at 14 kts was poorly chosen for this purpose, as a wind varying by 60 degrees should be reported as varying between those figures on the ATIS, however below 60 degrees, eg 120-170 degrees, unless that wind results in significant crosswind or tailwind for the duty runway (Rwy 16 in this case), the wind is to be quoted as an average from a single direction (so probably 140 or 150 degrees at 14 kts).