The greater GUI pages include many specific files. The inclusion code would be much shorter, more readable and better to extend for mods if it would just include the entire subdirectory.
This means some unused functions will be loaded, but that shouldn't be an issue at all.
The files may not overwrite each others functions to begin with.
When one GUI page is pushed on another GUI page, or if the user switches the GUI page potential states like in g_NetworkWarnings of network.js are lost anyway, so reloading it doesn't add any harm.
Also the common/init.xml is useless as it includes two common/ files which are already included by the GUI pages, so it should be deleted.