I live in IL, and my house has two layers of brick covered with a layer of 1" clay tile and plaster. There is no insulation whatsoever. There is no gap between the layers to blow in insulation or foam. My home is only 895 sq. ft. but I pay more than a 2,500 sq. ft. home in utilities. I've put new windows and doors in and two layers of R-30 insulation in the attic. Please, please, please help with any and all suggestions.
Shaun, unfortunately adding insulation isn't going to be an easy task, but it can be done. While it may cost a little bit, you should be able to recoup the money spent over time with savings on utilities. I am a little surprised that with two layers of brick and one inch of tile your heating and cooling costs are so high. While those materials don't have the R-values of fiberglass or spray foam insulation, they should be somewhat helpful in keeping energy costs down.
It sounds like your attic is in good shape, and with new windows and doors those areas should be energy efficient as well. I'm assuming that you did some research and found windows and doors with a high efficiency rating. Have you had an energy audit done on your home? It's possible you could have some air infiltration from somewhere that could be contributing to your high utility costs. You don't mention whether the house has a basement, but if so, that area should be insulated as well. It can be done on the perimeter walls if the basement is a conditioned space or you can install fiberglass batts between the floor joists. You may also want to consider spray foam insulation in both areas as it can usually provide higher R-values while taking up less space than fiberglass.
As far as adding insulation to the main level of your home and any upper levels, the best solution may be filling the walls with blown-in material. Many older homes have insufficient insulation in their exterior walls and sometimes none at all. When they have wood siding, small holes can be drilled into the siding to allow the blown-in insulation to be installed. The holes are then plugged - often with the same piece of siding that was removed. Unfortunately, with brick veneer and plaster this isn't an option on your house. However, it should be possible to use the same method on the interior of your home.
Whether your home has plaster, sheetrock, or even wood paneling on the inside of the exterior walls, the holes created to install the blown-in insulation should be able to be patched so that they're just about invisible after the material has been installed. Exterior walls usually have wood framing installed on 16 inch centers so figure on needing at least one hole every 16 inches. The hole size is normally about one inch in diameter. While the blown-in might not be quite as good as having fiberglass batts installed in the walls, it should help a lot in reducing your utility costs.