There are tons of papers available that would go with your midcentury home. Many people tire of a paper quicker than they are ready to redecorate and they can also look dated in a couple of years. Metallic papers were big im midcentury...perhaps a metallic silver paper? Are you also considering paint? You can get it in so many textures and a blue wall to match the blue in your loveseat would be lovely with some midcentury art and sculpture, or photographs on it. A mirrored wall with or without art or sculpture would also work with midcentury. These treatments are easier to adapt should you wish to change the look slightly from time to time. I would suggest replacing your stairrail with chrome or acrylic if that is in the budget...see how well the loveseat frame looks with the fabric? I hope you will post the "after" photos for us to see. Above all, enjoy the process!

I like @kelly's idea of picking a lovely fresh color of paint for the door. You can then bring it down onto the stair risers. Either a solid color to match the front door, or go wild and add some decorative elements to the risers with stencils. Or think of staining the door a great color and coordinate the stair railings and risers. I have an idea book put together for just such project that might spark some ideas for you. http://www.houzz.com/ideabooks/16700983/thumbs/Kathryn-Delany-s-Decorative-Stair-Risers

We got the IKEA shelves that are pictured in the butlers pantry photo I posted when we were on holiday in Melbourne, Australia. We don't have IKEA here in New Zealand! Hubby is going back over in May/June so will get him to get more of that sort of thing when there. We would pay about 4x the price for that sort of thing here in NZ. I need to work out what I will do now where the fridge was and there is the angle change (does that make sense?).

Looks like the dark window trim is trying to steal that beautiful ceiling's thunder. I have had both stained and painted trim. With stained trim I stayed with lighter colored, neutral/dusty wall colors as not to compete, lending a warm look. With light color, painted trim work, I could go more colorful and the trim really pops, Rooms look fresh and bright. Practically speaking: White trim required more frequent cleaning, but was much easier to repair and repaint the dings and scuffs. Polyurethaned wood trim required less maintenance but it was trickier, especially moisture and sun damage. Beautiful space, by the way!