Oh no ... low contrast are not always fail. Not at all. That's the Shabby Chique look!
ITA re the bottom left pinwheel ... If you're using that pattern, watch that the pinwheels have the contrast to let them show.
You might want to add another one or two fabrics to your mix, though you can get some lovely subtle contrasts with what you have. However, don't get too carried away with add-ins, as this is what your Grandma chose!! And you want to keep it "her" quilt! Have fun making it. What a special project to work on.