I think this is more correct, admins/mods should always be able to invite

lib/guardian.rb

@@ -176,11 +176,13 @@ class Guardian
     is_me?(user)
   end
 
-  # For now, can_invite_to is basically can_see?
   def can_invite_to?(object)
-    authenticated? && can_see?(object) &&
-    not(SiteSetting.must_approve_users?) &&
-    (@user.has_trust_level?(:regular) || is_staff?)
+    authenticated? &&
+    can_see?(object) &&
+    (
+      (!SiteSetting.must_approve_users? && @user.has_trust_level?(:regular)) ||
+      is_staff?
+    )
   end
 
   def can_see_deleted_posts?

spec/components/guardian_spec.rb

@@ -190,9 +190,14 @@ describe Guardian do
       Guardian.new(user).can_invite_to?(topic).should be_false
     end
 
-    it 'returns false when the site requires approving users' do
+    it 'returns true when the site requires approving users and is mod' do
       SiteSetting.expects(:must_approve_users?).returns(true)
-      Guardian.new(moderator).can_invite_to?(topic).should be_false
+      Guardian.new(moderator).can_invite_to?(topic).should be_true
+    end
+
+    it 'returns true when the site requires approving users and is regular' do
+      SiteSetting.expects(:must_approve_users?).returns(true)
+      Guardian.new(coding_horror).can_invite_to?(topic).should be_false
     end
 
   end