Many older/antique tops will lose their monetary value if you complete them. However that is your choice whether to complete it and use it, leave it as it is. :D:D:D
I would not store it in a plastic bag as it could draw moisture and mildew, nor would I put moth balls on the fabric. The moth balls could ruin/stain it.
Wrap it in acid free tissue, ball up the tissue so that it keeps the quilts fold lines from being sharp creases, and wrap it in the tissue. Do not lay it on bare wood, that can cause staining. Put it in a drawer, take it out and refold it every couple of months. You could put moth balls in the drawer if that is a concern.
I would love to see a picture of this treasure :D:D:D
Hint:don't hit preview when trying to download pictures :wink: