I must admit that i think they are missing a trick, and are probably too led by tight fisted accountants nervous aboyt free stuff.
The brilliant thing about M&S is that they have some really excellent food items and some good clothing items that could be used in conjunction with the card to get people to develop and reinforce an m&s habit. I would suggest free single high quality items for regular purchasers that are presented in store and show off high quality items..eg free small pressed cocoa bean bar with a lunch purchase or free gin bitters with £30 plus alcohol purchase, or free high quality cotton knicker pack etc They should be aiming for a 'fuck, these are good! no wonder I'm an M&S shopper' type reaction over and over again. This would reinforce brand, be distinctive and sought after and encourage use of the card. .which means more customer info.
once they have that customer info, good offer patterns will bubble up from behaviours. I think at the momemt the internal conversatio n is more like 'what have we got a lot of stock of? shall we get the card people to put it on offer' rather than the card people saying '60% of sparks card holders buy lunch once a week, and seek more fruit, we could get it to two or maybe four if we offer a health shake for sparks owners in Jan and Feb' and/or convert to clothes buyers if we offer a workout tee for buying more than 20 healthy lunches in Feb'
iyswim...!