To be able to easily create a sort of template project from an existing Visual Studio Project, I created the NuGet Source Code packager.

You're able to select the source code files you want to export to your NuGet package. The files are renamed to the .pp extension for pre-processing by NuGet when the package is installed. This takes care of the proper namespace in the new project.

The tool is open source and available on CodePlex.
http://nugetpackager.codeplex.com/