There are quite often mysteries and puzzles to solve in the world of the antique book collector, there are always questions of provenance, of publication, of authenticity of the work. However - there are never such deeper mysteries then when it comes to the subject of ghostwriters.
Ghostwriters - those who write for other authors or companies are in fact a common industry experience. Many non-fiction books, autobiographies and a wealth of other reference material are written not by the name on the cover, but by a talented young writer trying to make their way in the world. Several famous writers themselves worked either as copyists or ghostwriters, learning their 'chops' and earning money before they presented their own visions to the world.
Despite this, ghostwriters are often considered the bane of the collecting world - for the simple reason as we might think 'who are we really collecting?' Is this Tom Clancy book really Tom Clancy? The Queen of the ghostwriters is Carolyn Keene - or rather; the team of people behind Carolyn Keene, who wrote the Nancy Drew and the Dana Girls mystery books. Despite the ambiguity of their provenance, the Nancy Drew books were so popular, and important to so many people that they are still eminently collectible.
The very first Nancy Drew title, The Mystery of the Old Clock was important because it sought to marry elements of detective fiction with children's fiction - a technique that 'Carolyne Keene' used to great effect, and was latter appropriated by Enid Blyton for her Famous Five books. If you are lucky enough to find a first edition of The Mystery in good condition (Grosset and Dunlap 1930) then there is a clue as to whether the copy is merely a first edition, or is indeed a first printing. The first print-run of the books only had three other titles in the series printed on the copyright page which marks these books as worth over a thousand US dollars. If it also has a good dust jacket with its notable strong illustration on the front, then that price jumps upward considerably.
Otherwise, perhaps consider some of the slightly less-expensive Dana Girls books, published in the same range (1934-1979), with the earlier section (first series 1934-1968) being the more valuable. A first edition Dana Girls book, with a fine dust jacket would cost somewhere in the region of two to three hundred dollars - worth the price, and a joy to collect at over forty unique stories!
Keene, Carolyn. Secret of Red Gate Farm. Grosset and Dunlap, New York (1931). Plates By Russell H. Tandy (illustrator);First Printing, 1931: List Of Titles At Front Ends With This Title
Keene, Carolyn. The Hidden Staircase. Grosset and Dunlap, New York (1931). Russell H. Tandy (illustrator).
Keene, Carolyn. The Secret At Shadow Ranch. Grosset and Dunlap, New York (1931). 4 glossy black and white illustrations (a frontis and 3 internals) by Russell Tandy
Keene, Carolyn. The Clue in the Diary. Grosset and Dunlap, New York (1932). Russell H. Tandy dustjacket art and illustrations;
Keene, Carolyn. The Password To Larkspur Lane. Grosset and Dunlap, New York (1933). LAST TITLE ON JACKET IS THE CLUE OF THE TAPPING HEELS, LAST STORY MENTIONED ON DEDICATION PAGE IS THE PASSWORD TO LARKSPUR LANE
Keene, Carolyn. By The Light Of The Study Lamp. Grosset and Dunlap, New York (1934). 4 internal full-page illustrations on glossy paper by Ferdinand E. Warren, with the girlsreading note pictorial endpapers; The first Dana Girls mystery, #1 on dustjacket spine;Dustjacket flap and copyright page lists only the first three Dana Girls titles; The 3 pages of ads at the rear list the 3 Dana Girls stories, 3 Melody Lane stories and 10 Nancy Drew titles up to Larkspur Lane
Keene, Carolyn. The Clue of the Broken Locket. Grosset and Dunlap, New York (1934). 50c price on DJ flap; advertisements for Judy Bolton series on back and Dana Girls mysteries on rear flap; eleventh title in Nancy Drew series as listed on copyright page, with thirteen titles listed on DJ flap;back of dj lists toThe Mystic Ball in the Judy Bolton series
Keene, Carolyn. The Secret at the Hermitage. Grosset and Dunlap, New York (1936). First title to be written by Mildred A. Wirt Benson ;208 pages illustrated by Ferdinand E. Warren; Violet and green pictorial dust jacket lists five titles on front flap: Light of the Study Lamp, Lone Tree Cottage, Shadow of the Tower, Three-Cornered Mystery and Secret at the Hermitage.
Keene, Carolyn. The Circle of Footprints. Grosset and Dunlap, New York (1937). glossy frontispiece and 3 other glossy internal illustrations; Front flap and copyright page list through this title. Nancy Drew listed throughThe Mystery of the Ivory Charm (1936) on copyright page and rear flap
Keene, Carolyn. The Whispering Statue. Grosset and Dunlap, New York (1937). Illustrated by Russell H. Tandy
Keene, Carolyn. Mystery at the Moss Covered Mansion. Grosset and Dunlap, New York (1941). Russell H. Tandy (illustrator)
Keene, Carolyn. The Quest of the Missing Map. Grosset and Dunlap, New York (1942). Farah 1942A-1, the first printing, with 19 ND titles listed on the jacket, 10 Dana Girls, and 15 Judy Boltons
Keene, Carolyn. The Secret of the Wooden Lady. Grosset and Dunlap, New York (1950). First American Edition