Well this would not go down well in Australia where I'm from. Firstly, as others have said here, its incredibly insulting and patronising and aussie nurses don't take too kindly to being patronised. It also singles out nurses from other health professionals as being treated differently, which is unfair. I know plenty of medical officers and admin staff who are rude to patients.
Secondly, it doesn't look into or resolve the issues which are causing nurses to allegedly give negative customer service - perhaps staffing is an issue, or working conditions aren't adequate or staff morale is low for some other reason - these are issues which affect nursing worldwide, how difficult can it be for management to figure this out?
Thirdly, all this will encourage is insincere smiling and chatting - I am genuine in my interactions with patients and it won't continue if some stupid nurse manager is standing behind me with her cookie coupon.
If I worked somewhere that did this, I would refuse those stupid cards for coffee and biscuits. When I chat and have a laugh with patients and their relatives and help them above and beyond the course of my duties (as I know most nurses all over the world do), I do not want a reward for it, as I consider this my job.