I would say don't blur the wall at all, only the balloons further back; it just gives the impression of a low-quality render.
I like everything else, though, and think it would be quite nifty if changed in the way I mentioned!
create a depth pass and use a compositing program to blur it correctly.
you can create a depth pass by projecting a black and white ramp from the camera (this is also quite good for fog)
if you dont have a comp program then use maya dof i guess. but it works better than guessing in photoshop.