Polymer Dart as a SPA framework
I think Polymer is quite a good fit for that. I wouldn't necessarily go for "a Polymer element per page" but that might depend on the kind of application you are going to build. Especially in Dart Polymer it's a good start to make the root Element a Polymer element. You can for example keep the navigation and switch only a part of the view instead of the entire page (but that might be what you had in mind anyway)
You can also use dependency injection, which is a strong point of Angular.
The dirty checking might be better in Angular 2 but Angular isn't released yet and Polymer also has plans to improve here.