Since some modules use settings already (latest SVN, rightsmanagement & online), and more and more modules will later on (seeing the colors in settings ToDo-item), it is a good idea in my opinion to make the Settings.php module a core-module, move the get_setting function from rightsmanagement to settings and make sure all settings are requested & managed through that module.
This way you will have less redundant functions and if there's need to change a _setting function you only have to change it on 1 location.
Just my 2 cents.