It depends on your house. Wall hangings don't add anything appreciate to MY house, but my brother's 110 year old house, it makes some difference. This is especially true if the quilt is against a wall that takes most of the wind.
I find where I lose warmth is right around the windows (not the windows themselves - they are new), especially in a basement bedroom. I'm experimenting there. Just folding a quilt over the edge wasn't doing it. I'm making some simple quilted draperies that will extend about 8 inches on 3 sides of the window. Cotton and poly batting have an R value of 3-4 per INCH THICK, so I'm not sure how effective that's going to be. I do know draperies reduce draft.