As an Australian who also needs to travel vast distances to partake in Cunard (or other) voyages to the regions of the northern hemisphere I and DH love to explore and revisit, I empathise with the luggage dilemma. The solution is simple really: dress elegantly (or "formally") for each evening. DH only needs to travel with one dinner jacket (tuxedo) and formal trousers, and add a different bow tie and kerchief to change the look. I simply pack formal pantsuits, evening tops, several pairs of flowing culottes and one or two evening pants.
I also understand the "live and let live" philosophy, but here we disagree. I am of the firm conviction that what one wears in the evening sets the tone for the evening. I've often found it interesting to note that once a few couples dress elegantly, on any line we've sailed with, the next evening sees many more following suit. Sometimes, on non-Cunard lines, it's simply a matter of simple attire with elegant jewellery added, and the diamonds don't need to be authentic, just adding an elegant lifting of the attire.
Prior to our very recent and delightful two-week Queen Anne voyage, we enjoyed a three-week Med cruise on Oceania's new Vista. Each evening, we dressed for dinner, although admittedly DH was not dressed in his formal dinner attire, but in a jacket and tie nonetheless. Those same clothes served us well on Queen Anne later, with DH bringing out the dinner jacket (tux) for the gala evenings. He also wore it on one or two other evenings on QA.
On another note, but to add to other observations above, I find those who claim "ownership" of any particular experience, in this case the proud and revered Cunard line, are condescending in the extreme, and probably suffering delusions of grandeur.