Just remove pagename=event& and reset your rewrite rules…
$newRule = array('event/(.+)' => 'index.php?eventid='.$wp_rewrite->preg_index(1));
*template_include* is a filter NOT an action!
add_filter('template_include', array($EventpageCode, 'template_redirect_intercept'));
You can use *wp_title* function or filter to modify your page title.