What's the difference?
Dashes and Drama
The difference between a colon and a dash is pretty subtle: they can both serve to introduce a related element after the sentence, but a dash is a stronger and more informal mark than a colon. Think of a colon as part of the sentence that just ambles along. "Squiggly has two hobbies [and, now I'm going to tell you what they are, colon] cooking and bothering Aardvark."
A colon informs readers that something more is coming along. The words after a colon define or clarify what came before the colon. The two hobbies before the colon are defined after the colon as cooking and bothering Aardvark.
A dash also introduces extra material, but, well, a dash is quite a dramatic punctuation mark. A dashing young man is certainly not an ordinary young man, and if you're dashing off to the store, you're not just going to the store, you're going in a flurry.
A dash interrupts the flow of the sentence and tells the reader to get ready for some important or dramatic statement. If you added a dash to the "hobbies" sentence it would conceptually read something like this: "Squiggly has two hobbies [wait for it; wait for it; dash] cooking and bothering Aardvark." Wow!
Normally, you don't want to follow a dash with something boring or mundane, so given that there isn't really anything exciting about Squiggly's hobbies, a dash may not be the best choice here. It would be a better choice if that sentence were part of a mystery novel where Aardvark has been attacked with chocolate pudding, and the police were investigating Squiggly's involvement. Then it could be a dramatic announcement that Squiggly's two hobbies are cooking and bothering Aardvark, and a dash would make more sense.