The Collector's Edition of MoP includes the usual list of goodies. An Art book, a behind the scenes DVD, A mouse pad, soundtrack, the game itself, and a in game mount and pet.
Nothing stands out in this collection as a must have for me. It's basically the same package each time, and now that a digital version is available, I really don't see a point. There is nothing new and exciting.
If you are a hardcore collector of WoW merchandise, this is for you, however, if you don't feel the needs to have a physical copy, the digital version is the way to go.