Wow. I'm kinda surprised so many people didn't like the wool applique. I was going to suggest more of that & maybe some beading in the redwork. And to keep the one applique Spring/Summer related & make the other one Fall/Winter themed.
From my view, the issue with leaving it plain is going to be how to quilt it. It can't really be quilted in a contrasting color or it will compete with the redwork -- so that means you'll have very large borders that -- especially the patterned fabric -- will not show the quilting much at all. I think at this point, I'd maybe go with a thin layer of trapunto just to help break up the borders a tiny bit with the quilting.