My advice - have several, but don't buy them if you don't have too (unless they are at yard sale prices or you have checked it out from the library so many times you can literally hear it calling your name every time you walk in the library)
USE YOUR LIBRARY!!!!!! This is an excellent way to 'test drive' a book before you take the plunge. Another thought is if you have checked out the book more than 3 times, AND have enjoyed using it (not just looking at the pics), consider having it on your birthday, Mother's Day, Easter, or Christmas wish list (of course you do have to let people know it's on that list for this to be effective). This way your family gets you something you love and you get something you don't have to return for a smaller (or larger) size.