I like the idea of the circles at the corners. If you make a large circle then a smaller circle inside it they will look like coffee saucers and everyone will think you planned it that way.
Even though you have done stitch in the ditch along the seams the reason for doing the corners is to catch the batting between the cups. I think if you get the larger areas stabilized your should be OK under the cups. Very cute quilt. You are quite talented.