I always used to save syns like you're describing and lost weight.
My New Years resolution (one of them) was to only have alcohol one day of each week in January, and to stick within 5-10 syns on a non-exercise day, and 10 - 15 on an exercise day (even the drinking day). Needless to say, it's got me off my bum on the day that I've been drinking. The rest of the time I usually find myself wondering what to do with my syns, as I'm not used to using them on food stuff!
Been handy this week though, as have been without kitchen facilities!