Conditional 404 response based on inclusion of /node/# in URL
What about using hook_init in a custom module?

function hook_init() {
    // check arg(2) is empty as otherwise will block node edit and delete pages
    if(substr($_SERVER['REQUEST_URI'], 0, 5) == '/node' &amp;&amp; arg(2)=='') {
        die(); // to stop completely
        //return drupal_not_found(); // to return 404 page
        //return drupal_access_denied()(); // to return 403 page
    }
}


Saying that it would be quicker to block these pages in .htaccess...