if no one ever manages to break contracts with demons (or at least, hardly ever) there has to be a lot to Dean getting out of it, more than just someone else offering themselves in his place or something like that, and I can't help wondering if this is a piece of the puzzle.

Oh. Okay, I don't mind it being a small piece of the puzzle, but I'd hate it to be a large basis of the solution. As I said, I want the solution to be something they do, not some trinket they they find. In all honesty, I think it should involve some sort of sacrifice. Nothing as simplistic as Sam trading his life/soul/whatever. But I think that whatever the boys do to stop it will have to involve someone losing something they value or perhaps have to live with the pain/guilt of something they've done. They may think the price worth it, but some sort of price will need to be paid. Salvation doesn't come cheaply. Or it shouldn't IMHO.

(But oh, you DO have a point about the guilt factor, if it does turn out that way! Like he needs more guilt ...)

It would also be a bit too much like his major guilt of early season two. It would seem a bit too much like a rehashed storyline to me. So, I don't like it from a dramatic standpoint, even aside from the fact that, as you say, Dean scarely needs more guilt.