Since you are using this class for the Admin area, the $_GET['main_page'] reference is, as you mention, completely irrelevant, as the Admin doesn't use the main_page parameter in its URLs at the present time.

You'll notice that the default behaviour for this in the current admin version of this class is to use basename($PHP_SELF) instead.




As an aside, in the catalog/storefront side of things, $current_page_base is the variable available to reference for the currently-displayed page. Inside a method it'll have to be declared as a global in order to use it.

As to the coding recommendations, you are correct that there are some things to tidy in that file. Some have been done in the v1.4 code under development. More will follow in due course.