[Plugin: WordPress Admin Bar] using in the admin backend for non-admin users

As you discovered, all settings are on a per-user basis. However you can modify this plugin’s defaults using a filter. Drop this in your own plugin or your theme’s functions.php file:

add_filter( 'wpabar_defaults', 'xyzzy_wpabar_defaults' );

function xyzzy_wpabar_defaults( $defaults ) {
	$defaults['show_admin'] = 1;
	return $defaults;
}

thanks!