Having been in the old house restoration business I can tell you that some of the old insulation is of poor quality compared to today's standard. They used spun wool, fire retardant treated newspaper, and other products. Removing these which have settled and replacing with today's fiberglass will make a world of difference.Curious here. What would be the difference or benefit from sucking out the old and blowing in new ? Is the new stuff better than what as there ? I need to add some to mine also.