I have exactly two special editions with me. Batman: Arkham City and Hyperdimension Neptune. And I have both of them for one single reason: They were the exact same price that the normal editions had. It is very hard to justify the jump in the price by whatever come included in the box for special and collector's edition of any game.
Most come with pretty useless things if you consider useful some thing that can apply to the game. That extra DLC can be bought separately and many times at cheaper price when compared acquiring DLC+basic game VS special/collector's edition.
All the rest is pure decorative things. Maps, PVC figures (which I would like to have, but the price asked is far more what those figures are worth), cards, some jewelry. Others are nice, like art books, soundtracks and posters. But hardly something worth the price.
Space is other problem. You need a lot of space to exhibit those things. If you don't have, paying for them and keeping inside a box under your bed basically kill the purpose of having a collector's edition, that is to show off all the cool little extra things in the box.
Of course, if I had money and space, I would have a lots of collector's editions, because I like to show off as much as the next person. But I don't have this extra cash neither the space to do it. So, unless the collectors edition are really amazing, from s a company I really like, I will just say how cool they are, and get the basic game. Because that is why we buy games, right?