Just in case there's still anyone out there who isn't following Artur Malabarba, he has a nice post on something that I had almost forgotten about. It turns out that you can set Emacs variables on a per directory basis. These directory-local variables are especially handy for setting project variables by adding them to the root directory of your project.
The process is easy and Emacs will guide you through it if you call
add-dir-local-variable. You can even arrange to have a bit of Elisp code executed so the facility is reasonably general. Take a look at Malabarba's post for the details. If you're working on projects where you'd like to have a special configuration, this could be a real help.