A useful way of deciding if something fits into a Project or an Area is the Progress / Maintenance distinction. Progress tasks move you forward, such as installing a new machine in a factory. Maintenance tasks are the hygiene tasks that stop you slipping backwards, such as clearing the factory floor of rubbish.

Something I just thought of, more applicable to a tool such as Evernote that allows you to have tags as well as folders, if something in a project is about the project management of that project, tag it with "Project Management" and you will know to look in the "Project Management" Resource folder for related material.