Do you have a picture? Window dressings are layered all the time, so I don't necessarily think it would be a faux pas, but recommend you consider solid drapery panels in either burgundy or beige to coordinate and to just frame the window/new shades. Panels would look a bit more updated than a valance. If you go this way, be sure to hang the rods high and allow the panels to fall straight to the floor (no tie backs).