I think you would have to evaluate the attic area. Is there any moisture problem visible? Is there any moisture trapped in the first layer of insulation that could damage it? do either layers of vapor barrier actually seal off an area or are they just laid next to each other? How do the energy bills stack up? These are things I would weigh in addition to the cost of pulling it up and doing it right.
I do prefer to have it done right, so I may error on behalf of redoing it if it was my investment. I think you should call it out and say what you see and let the investor make up his/her mind on what they want for their dollar.
Rick

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Rick Sabatino
Sabatino Consulting, Inc.
Oak Park, IL