I worked for M&S for 17 years until I had my last child which made me utterly unworthy to them. They are so staggeringly shit at flexible options (I was in management). But that's another story 
You're so right about the Sparks card, its rubbish but sums the company up. Too many people making decisions centrally who have zero qualifications or skills, its a company run on knowing the right people. Whoever came up with this scheme almost certainly has no marketing skills or experience but instead is good mates with someone senior.
I can totally believe that the staff hate the card too, the stupidest thing of all is that their employees are one of their most important customer groups. There are lots of people who go to work for M&S as they want the staff discount which to me is fair enough - at least they want to buy the product!