What beautiful treasures, even to display one at a time would be wonderful, I saw in a quilting mag once where the old quilts were repaired with a fine layer of soft bridal 'Tulle' appliqued over the worn piecing, ( not the scratchy nylon net type) You could hardly see it at all as it comes in ivory and white and they had used the ivory. This method would be saving the quilt in it's original state, no fabrics to match, no unpicking and no added weight to the quilt as the Tulle is extra light. This is if you were wanting to use them of course to help strenghten them, if you are thinking of displaying them only, then I would leave as is.
Gal