Advanced Search form_alter

Currently in my module, I have the following code :

function mymodule_form_search_form_alter(&$form, $form_state) {
  if (isset($form['module']) && $form['module']['#value'] == 'node' && user_access('use advanced search')) {
    $form['advanced'] = array(
      '#collapsible' => TRUE,
      '#collapsed' => FALSE,
    );
    unset($form['advanced']['type']);
    $form['#validate'][] = 'node_search_validate';
    dsm($form);
  }
}

So, dsm($form) prints that form at the top of /search/node, but the 'advanced' array and sub-arrays don't render properly - i.e. they consist of the changes made in this module and nothing more - and have no effect on the form itself. I also have Devel printing the $page array, and comparing the two, it appears that I am trying to alter the correct form.

Anything I try to do to edit the advanced search form has no effect, no matter what. I've been able to render the form uncollapsed using js, but seeing as I'd like to do more with it and require a form_alter to do so, I need this to start working soon.