|Voted Best Answer
Steve made a good point. Also, while it isn't required to remove the old insulation you can check the ductwork, wiring, etc. with the old stuff removed, You can also spray foam around all openings and holes in wall top plates to better seal your home as Steve was pointing out. My concern is the potential for mold spores you mentioned in your question. If you suspect there are any get a good company in to remove the old and clean the attic. Another concern is asbestos. Your home is old enough you could have it in there and that's worse than mold if released into the air.
Todd's Home Services