OP, I think you're overlooking the attitude towards conspicuous consumption of certain kinds in some sectors of society -- an ancient hand-me-down uniform and battered trunk at a certain sort of public school, for instance, indicates either an older sibling or other relative also attended, giving you a pedigree, OR just that you have the 'right attitude' and are so confident in your social position you can ignore appearances. A spanking new get up and gleaming designer suitcases indicates (viewed from this angle) nouveau riche insecurity and trying too hard.
I remember a newspaper article about Kate and Pippa Middleton's schooldays, containing apparently innocent but in fact deeply bitchy comments from another (purported) parent who'd had children at Marlborough at the same time the other parent said the Middleton parents made everyone feel inadequate because the girls were always perfectly turned out in new school get-ups with perfectly sewn name tapes, perfect luggage and smart, brand-new sports equipment and that they always brought the most elaborate picnics to school sports days etc.
It looks like admiration, but the subtext is 'not quite PLU, trying too hard'.
So, the appearance of frugality (at least in certain things) can in itself be a class marker.
Look at how often the same shibboleths are trotted out on here about the 'genuinely UC' their battered cars, their hair-covered ancient clothes etc going along with their 'lovely manners'. Ditto for the disapproving accounts of the nouveaux riches conspicuous wealth, designer gear, over-elaborate grooming, pushiness etc.