What M&S used to give us was a great deal. For a reasonable price, you'd get well made clothes with good designs and using quality materials. On top of that the customer service was first class and if you had a problem, you knew you could take it back and they'd be interested in what had gone wrong (because it was unusual).
There was no internet and so they could guarantee that lots of people would visit their stores and they'd be able to shift whatever stock they took in - because it was good quality and a good price. And because they sold so much, they could keep costs down, enabling them to keep their prices reasonable. So, a virtuous circle.
I would be willing to bet that the current board would love to return to those days, but its so much easier said than done. So what can they actually do?
IMHO M&S could and should get rid of the hideous designs and awful layouts. They should re-focus on what made them their reputation. If they massively reduced the number of lines they carry but upped the quality and design, then they could take advantage of the customers, like us, who still remember their reputation. However, if they leave it too much longer, we'll all have moved on and won't be coming back.