You are track of a useful idea here, but the ceiling space is not the place to use it. I have actually asked our local waste management municipality if it's realistic to pull a stream of waste styrofoam from the landfill sorting process. While they haven't asnwered me, because of styrofoam's low density, separating it should be straight forward.
The ceiling space is open. Styrofoam burns obnoxiously, as the comments above point out. When it is used in a building, most codes require that it have a fire protection barrier equivalent to 1/2" gyprock, and that's using it as a sheet material.
Here are a few ideas. Run with them, and remember me when you get rich.
Chop to a uniform size, and use as an adjuvant to lightweight concrete. This would essentially replace vermiculite.
Similar to above but use it as a spray on insulation on the outside of a foundation.
Chop, clean and quickly mix it with acetone, possibly diluted with water, and press into sheets. These would have drainage built in, but despite the air circulation would still be several times the insulation value of dirt.
Fuse the chips together with heat, and press into 1 x 1 x 4 foot lego blocks. While not code for houses, they may work very well for utility buildings. In the block making process score grooves in them, so a stucco coat can be sprayed directly on them without the need of mesh. Stock piling a million such blocks near New Orleans may help for emergency shelter next time a hurricane catches them with their shorts around their ankles.
Similar, but as part of the fusing process coat them with sand, or finely ground beer bottles. This would protect the block from UV, possibly give them an attractive finish, and because of the sharp edges discourage rodents and small children from messing around with them.
