Hello, Yes it would make a difference if it can be done correctly, but getting the blown in insulation to fill in completely is almost impossible. We have tried this several times and it still leaves voids in areas because the blown in insulation get hung up on wood, nails, wiring and the existing fiberglass insulation. Here is a question, how about insulating garage? Would be easier, and even more easier if not already done, then adding small amount of heat there? This will keep you upstairs a bit warmer.
Plus you can have a toasty car in the a.m. Mrs will luv you forever! lol Hope this helps. GregC