Well the reality of collaboration is, if it's not with a friend and the details don't matter, it has to be a mutually beneficial occurrence.
It's easier if you're the larger channel. Most people will want to work with you just for having a lot of subscribers.
On the other hand, if your are near equals or you are the smaller channel, it is better to present your idea in the best light possible and you'll want to answer this main question.
"How does working together benefit us both?"
If they can see that you're passionate about what you do, they digg your idea, and they know they'll get something out of it, they'll want to work with you, and if not. Well. Move on.