What is hanging on the wall by the dining table? A mirror? TV? It's hard to tell because of the glare, sorry. If it's a mirror replace it with art. Not many people want to watch themselves eat!

A tall bookcase between the two rooms in a stain shade to match the table would work but edit it carefully, you don't want to crowd the shelves.

Yes, art will add to your room where as a mirror just looks cold and uninteresting.

A large plant--tall like a palm could work on the wall.

You need to be careful about just adding a piece of furniture on that wall. It could look like you're just filling space.

Your picture is too dark. Can you include more of the living room area?