Art on the walls will help a lot. and getting rid of bulky furniture. Might look at these, they come in all colors, black green red,grey

Try to find some 5 year old magazines and you're all set :>)

Look at area rugs for the space connecting the chairs and again, some prints on the walls.

Sitting in a waiting room is always depressing. Maybe adding some bright plants or flowers would make it a little more inviting. Also, I would put all the seating on one wall, as opposed to having patients sitting directly across from one another looking at each other - that is sometimes uncomfortable.