I’ve responded to this in the plugin group. To some extent What you are asking for is already available on the standard BP menu – and at this time I wouldn’t probably advise using the adminbar plugin as it checks for WP 3.0 and then uses the newer menus these new menus have two huge flaws sadly; the first is that they don’t know that pages are children and thus don’t provide the ability to code as drop downs and they also make it hard to remove the parent ul .
The present BP main menu uses wp_list_pages the code in header.php allows for parameters to be passed, if you set the ‘depth’ paremeter to a value other than zero then it will include child pages but you have to then style those as drop downs if that’s what you require.