Your 'D' edition probably has 28 pages. The spine and the MMC notation was common on the Disney books. You would value it the same as a gold binding for a "D' edition. A guidebook might be helpful but probably not for the spine change. You cannot use LGB guidelines for other books published around the same time as they do not have edition or year identification in most cases.
I recently purchased a stack of books at auction and among them is a 1950, 'D', Mickey Mouse's Picnic. It has the red foil on the binding, along the bottom of the front cover it says "A Mickey Mouse Club Book" and it also has a "seal" next to the D15 and price of 25 cents that states "official Mickey Mouse Club". I cannot find anything about this particular edition anywhere online.
A point in the right direction to find out about this book would be great!!
Oh, and another quick question: can the way the printing/edition determinations used for LGBs also be used for say.....the Rand McNally Elf books?? I have a few hundred of those too and need to get an idea of what I have.
Thanks for any help!! This site is awesome and everyone is so helpful!!