I'm not married so I can't say much from personal experience. It does seem that poly itself isn't the cure but the work people do on themselves. In the last few weeks, I've been getting some perspective on the last 8 months and my first experience with poly. I'm realizing that the relationship I walked into was no where near as healthy as I had thought it to be. And that they weren't interested in doing that work and introspection. I don't feel jaded towards poly because I realized that they were never all that on board with poly in the first place. I do feel cynical towards relationships in general... but I suppose that will go away eventually.
That's one of the things that drew me to the poly community/lifestyle. I am very introspective and what not. I love how much people that do poly all tend to do a lot of that and don't shy away from it or think it's silly. I wish that more monogamous couples did that kind of soul-searching as a regular part of relationships. Scratch that, basically, everyone that interacts with other people should utilize that skill.