How to make a Feature available only to certain Spaces?
The features for each space are configured via the spaces_features_form() function. You could implement hook_form_alter() to selectively and conditionally remove features from specific groups.

function MYMODULE_form_alter(&amp;$form, $form_state, $form_id) {
  if ($form_id == 'spaces_features_form') {
    $space = spaces_get_space();
    // Populate the array with hard-coded NIDs, or whatever logic
    // needed to determine if these features should be allowed.
    if ($space-&gt;type == 'og' &amp;&amp; !in_array($space-&gt;group-&gt;nid, array(...))) {
      // Hide features foo and bar.
      foreach (array('feature_foo', 'feature_bar') as $feature) {
        $form['spaces_features'][$feature]['#access'] = FALSE;
      }
    }
  }
}