I do not think you will go wrong in either option (Garden Grocer or no Garden Grocer*). If you plan it out fully, you can probably get by with using some snacks as meals. The Yak and Yeti offers that chicken stir fried rice as a snack -- DW, DD12 & and I love it and it only costs one snack credit. There are other good snacks that you can stretch to lunch meals. We have not used the dining plan since they doubled the snacks though. Here is an article I found helpful
http://www.couponingtodisney.com/making-your-snack-credits-count-at-walt-disney-world/ We always have come in waayy over on snacks and end up having to load up on bags of candy for gifts for friends at home (although this does earn us browny points with our friends

) and that was before the doubling of the snack credits. As people have pointed out, if you can figure out how best to use a snack credit for breakfast that may be the way to go. LOL, however (there is always an however!), we have always used the Garden Grocer for some breakfast items such as bananas, yogurt, pop tarts or cereal and milk. The GG has items that you can by one of (bananas/yogurt/etc.) The big reason though why we use the Garden Grocer is that they carry wine and beer * (unless I have missed this,
Amazon Prime does not offer alcohol). I will get a 12 pack of beer for me and 2 bottles of Chardonay for DW. You should be able to get these items at a premium from the resort store. Here is a website regarding POFQ
http://www.portorleans.org/jacksonsquare-store.php While on vacation we love to relax at the end of the day and have a glass of wine/beer to talk over the day and discuss the next day's options. For me, the Garden Grocer is extremely reasonable in its pricing.
I would advise doing the math. Since you are paying an arm an a leg for your vacation -- if it comes in close -- do whatever is more convenient. You are on vacation!