I think I remember you asking about your copy on the eBay forums and I replied with a copy on addall. Probably the same copy discussed here. We have been selling books on the ABE site for 10 years now and have a few listed. It has been said by many that “just because a book is old, does not mean it is valuable”. There are many factors to determine (as Skinny talked of). The overall condition, cover and text. The rarity of the book, subject matter, copies printed, author, Illustrator, type of binding, the writing itself. We have ‘new’ books that don’t sell. They are poorly written or have been written and rewritten.
Then there are books like the family bible that you would never put a price on. In a book store the bible is a hard sell, (no other book has been printed more often), but the sentimental value of a family bible or any other book, far outweighs the monetary value, and the cost of rebinding a tattered cover can run in the hundreds so you have to determine value ‘as is’ or after it’s restored.
Famous authors, 1st editions, dust jackets, many factors to help determine values. Yours, as you state is unique, and does have value but has some condition problems and also keep in mind that just because you might find another copy and that copy is listed with a high value, it is still on the book sellers shelf. Value is also determined by what the buyer is willing to pay. Sorry, I do ramble on. I do love books. I have a hard time tossing a book even if it’s worthless. I send a lot of books to good will. Enjoy your find.
"The man who does not read good books has no advantage over the man who cannot read them."
- Mark Twain (1835-1910)