Fiberglass insulation allows much more convection than blown in stuff, so in the end run is less efficient than what you have. From a fire prevention aspect, did they build a fire wall between each unit in the attic? This would be probably a stud wall with 5/8" or more fire resistant drywall on each side.
Are all of the units identical in size? Do you know if there is any insulation in the dividing walls?
Look at www.insuladd.com. You may not like the texture, but it has some sound engineering support.