How to tell if Views cache is being rebuilt during views_exposed_form's hook_form_alter()?

hook_form_alter() for views_exposed_form runs whether or not the exposed filters form is going to be delivered from cache. Since I'm doing some heavy calculations for each parameter (calculating the results if the parameter is added), it would be nice if during hook_form_alter I could know if the views_exposed_form form is going to be delivered from cache as to avoid the expensive calculations.

This is what I've come up with so far by looking at view.inc.

function views_depth_counts_form_alter(&$form, &$form_state, $form_id) {

  if($form_id == "views_exposed_form") {
    
    $view = $form_state['view'];
    // Taken from view.inc line 709
    if (!empty($view->live_preview)) {
      $cache = FALSE;
    }
    else {
      $cache = $view->display_handler->get_cache_plugin();
    }
    if ($cache && $cache->cache_get('results')) {
      vpr('Used cached results');
    }
    else {
      // Do some heavy calculations
    }

$cache->cache_get('results') returns NULL here even if it doesn't later in view.inc. I see that in views_plugin_cache::cache_get() calls views_plugin_cache::get_results_key() and I think the discrepancy is in what $this->view->build_info gives to $key_data on in views_plugin_cache.inc on line 252 which results in an incorrect key generation during hook_form_alter().

Ideally if a cached version of the exposed form was going to be used, the views_exposed_form wouldn't even be built. Perhaps that's an easier problem to fix but would require a more intimate knowledge of Views 2 internals than I have right now.

Any pointers from the Views gurus?