Bizarrely, I saw this feature in EL in the hairdressers today for the first time ever, so can express an opinion on coincidentally zombified thread (the only "woman's magazine" I normally read is Stylist, which has solid feminist principles, a Lucy Mangan column, and is free).
I think you're giving it a bit of a hard time. Apart from the (to me) baffling obsession with handbags stamped with LOOK AT MY LOVELY MONEY on them in 72 point type, the clothes are mostly medium to high end High Street, rather than designer. Obviously not everyone can afford to get clothes from Whistles or Jigsaw or even GAP and Top Shop, but they're not the sole preserve of oligarchs' trophy wives. And the looks they are wearing are realistic and easy to copy from New Look, H&M or charity shops if you're interested in doing it - just because they're spending a thousand quid on jeans, a top, a scarf, boots and a handbag doesn't mean you can't achieve the same effect for a tiny fraction of the price (admittedly in my case I'd need hair extensions and a live-in professional blow dryer).
I think the school run dressing "thing" is a side effect of the Cranford law. The ladies of Cranford didn't dress up to shop in Cranford because the only people who'd see them were their friends, who already knew what they looked like. And they didn't dress up to go to London because no-one they'd know would see them (this is why so many people dress so appallingly on holiday). It's that middle ground of people who recognise you but don't "know" you that causes the problems if you're that way inclined, and the parents of your children's friends are very much in that class.