Hi there! You only have to worry about that blank space just above the piano - the part of the wall that is at human level. Don't worry about the upper half at all.

When I look at that wall (and your room,in general), my eye wants to see a fun and colorful piece of modern art, in about a 40"X30" size. The bottom of the piece should be 6" to 12" above the piano. This will "connect" the art and the piano, so they read as one unit.

Have a look at the works of Meghan at Fire Bonnet Designs on fineartamerica.com. Her work (as well as all art offered on this site) is available in several sizes, and is reasonably priced. Showing below one of my favourites.

Btw, I LOVE the teepee - lucky kids!

I would love to see a big canvas with the piano score of your favorite song up there.

This is a little more than artwork but would look amazing on that large wall. Water walls are not only pleasing to the eye but they also help clean the air by attracting dust particles. Check out more at http://www.luxewaterwalls.com/