Grand Case is almost completely restaurants - definitely not a shopping mecca on St. Maarten/Martin. We didn't actually find the shops there, but we didn't look very hard either. There are quite a few shops in Marigot, and obviously a huge shopping area in Phillipsburg.
If you're considering dining in Grand Case on your cruise, I would highly recommend it! We had a fabulous lunch at Le Tastevin, a prix fixe 4-course lunch (3-course and ala carte also available) with a different wine accompanying each course, at a lovely table overlooking a small beach and the gorgeous Caribbean. The manager let us keep a copy of the menu, so if you have any other questions about the food or the prices, let me know!
Keep in mind, however, that most of the restaurants in Grand Case are not open for lunch, at least on Tuesdays when the Magic visits St. Martin. Our first choice was actually Le Cottage, but alas, they were not open for lunch.
April