I agree with mckwilter -- museums are a wonderful resource. The curator in charge of textiles has many resources, including a circle of contacts, available to help. It seems that value in antique quilts is dependent upon condition, workmanship, pattern, and provenance. A textiles curator can evaluate those things. Another item they consider is the rarity of the design. There are some patterns that were so common that they are of little interest to collectors. On the other hand, if a person is a decorator or operating a bed and breakfast with a vintage theme, they may welcome another double wedding ring or Sunbonnet Sue. That buyer will look for a quilt that will have durability.
We would love to see pictures!