chris, sounds like you've got a comprehensive solution there :)
just a quick update from where we ended up: if you open a solution referencing both the projects referencing nuget dlls, and the projects that create those dlls - all you really need to do is change the dlls references in your shell project (ie. the windows app or SL app) to project references. This allows you do debug into those nuget projects, make changes, benefit from resharper refactoring etc. If interfaces dont change, that's all you need to do - if they do change you may need to change some of your other nuget-dll references to project references.
In general though, very simple! Once you've checked in your nuget projects & re-published, flip the project references back with a nuget update, re-test and you're good to go