Decorating happens where the people live. Lots of folks are closing in those massive open rooms and making a media room upstairs. Heating a wasted space isn't always all its cracked up to be. There is plenty going on below that space - in fact, a little to much, IMO. I don't get those blocky built-ins. They are just too chunky and country looking for your stylish architecture.Remove them and install lighted glass shelves with a marvelous collection of something you love - vintage silver pieces, art glass, or an interesting collection to keep the eyes in the people part of the room.

I would do a wallpaper with a soft, vintage pattern. You have an eclectic mix of styles in these rooms and I think something calm and classic would look really interesting ... as well as highlight the wonderful natural light in there and not compete with your more bold elements. Just an example of the style I mean: (Source: https://www.studiodb.com/residential/park-avenue-residence) And I love a big round mirror over it. It would be amazing at reflecting the natural light and your chandelier. (Source: House Beautiful) https://www.finestwallpaper.com/store/p6571/C.F.A_Voysey_-_The_Merle_Wallpaper.html Normally, I’m all for going extra bold with accent walls, but your house has a very peaceful, serene feel, and I don’t think it needs a jarring wallpaper print or color. ETA: Grasscloth is another idea — it comes in a variety of colors.

Create a pattern of each of them, in paper close to the green color, then use painters tape to attach the paper in different patterns to see what might work. Here are some ways to try: I like the 1st one with the shelf under it, which might work well with your wall. Pull the sofa out far enough that no one bumps their head on anything.

I agree with the advice to concentrate on the "people level" for now. More people level lighting, larger lamps, people level art, properly sized rug, another layer of window treatments. If the people level is fully decorated, the tall wall will look light and airy, not bare. This room has a similar wall, notice that the high part of the wall is not decorated. The room looks cozy because the people level is nicely decorated.