Is the first picture what you would see when you walk in the room? I would move the bookshelf or at least get one that is not slanted....it creates a big visual block. As for the window, I would frame it with a window treatment, move the plant, and add a bench and some pillows.

As for the blank wall space, I would consider a gallery wall with a variety of pictures and art. Or just opt for a large piece of art. I would put the buffet or side table on the same wall as the couch.

between the pictures, I'd get a low lying shelf or sideboard with a nice visual piece above it to draw you into the room. on the walls in the dining room, mirrors of different frames, shapes, sizes can be fun and make for appeal. mirrors will also make the room appear larger

For the wall between the windows how about a gel fuel fireplace. They have some that actually hang on the walls. I think one in a stainless steel would look nice.

Like the wall hung gel FP idea and agree you need to ditch the ladder shelves - very dated and don't you hate dusting them. Set your dining table on a rug that is 4 feet longer and wider that the table. Then add a floating buffet where there is room - either wall, but just so it isn't crowded to move around the table when diners are seated.