Hi, Dreamer1990!
Personally, if I'm going to pay an extra $7 for a Collector's Edition, I would much rather have a longer bonus chapter than wallpaper, clip art and sound tracks. Some of the newer games also have a section where you can replay the puzzles. I find that useful because I sometimes tend to skip certain puzzles, so I can try and solve them after I've finished the game or replay puzzles I really enjoyed.
The bonus chapters are sometimes an extension of the main game or take place prior to the main game but, as Marian has already said, if you buy the Standard Edition, you won't feel as though you're missing anything.
Enjoy "Otherword" if you decide to buy it. It's a wonderful game!
Susan