I took a cake baking class once where we made maple buttercream and the instructor insisted that any maple syrup other than Grade B was simply "finishing syrup" — meant to be used on pancakes and nothing else. So if you're just drizzling syrup over your oats, pancakes, waffles and crêpes, do you really need to consider the grade?
As with most things, there is a short and long answer. If you have young kids and you're making breakfast for them, the short answer is no. Will they likely taste the nuance beween grades of maple syrup on their waffles? Probably not. Perhaps you wouldn't care if they could either way (as someone sitting here without kids, I imagine there's a whole host of other things to worry about rather than what your child thinks of the flavor of the maple syrup you buy). The long answer: you can definitely taste the difference between a Grade A maple syrup and a Grade B maple syrup. For recipes where the flavor really matters (baking granola, cookies and cakes), I only use Grade B because it has a much more complex maple flavor, often with hints of caramel. Grade A maple syrup really is perfect for pancakes or cocktails: it tastes jupst maple-y enough to get by.
Of Grade A syrup, my favorite maple syrup provider, Stannard Farms, has this to say about the whole thing on their website: "Vermont maple syrup is graded by color. Grade A Fancy is the lightest maple syrup - it also typically has the lightest flavor. Grade A Medium Amber is slightly darker and has a little more flavor. Grade A Dark Amber is darker still and is great on vanilla ice cream. Grade B is very dark indeed - this is some of the best maple syrup out there, if you can get the good stuff."
So there you have it. Generally, the darker the syrup, the stronger the maple flavor. If you're just looking for a subtle smidge of maple or cooking for kids who won't know the difference, use whatever is easy to get ahold of. But if you're making a recipe such as a morning souffle, custard, muffins or quick bread where you really want the most special nuanced maple flavors to shine through, Grade B is really your best bet.