Even the base LS FE1 control arms are aluminum on the HHR, unlike the cobalt, so there is probably no reason to upgrade them.
Powell sells upgraded control arm bushings for the cobalt ss, not sure if they fit the HHR but I will find out, hoping to head up there in march for the customer appreciation day. He often has some control arms on hand if you need them, maybe you dont want to press the CABs in/out yourself?
And he recommends the pedders springs with the OEM SS FE5 shocks and struts. Not sure about the front swaybar though, as it can increase understeer if its too stiff. Adding the adjustable Powergrid endlinks could be a good option.