I have a 1961 home with 4" walls. I opened up a stud cavity and could see
that there is about 1.5" or so of fiberglass with kraft paper against the
sheathing. So there is about 2" of dead air space between the drywall and
kraft paper.

I had a proposal from an insulation contractor to blow in cellulose to fill
the area between the dryall and kraft paper. I am concerned because they'll
be insulation, a vapor barrier, and then more insulation.

Will this cause a problem. Would the extra insulation be worth the trouble?