Pull out one of your switches or outlets and see if it's insulated BEHIND the box. If it is then use your foam to finish the perimiter. If that doesn't work you can buy those foam gaskets to put at the receptacle / switches. Those do work well, but foam insulation can't hurt.
Do you want it your way or the right way?
I did that around mine, including putting 3m Window film over some windows in my living room, and it has helped. My furnace does not cycle that much, as it did before I did the foam around the outlets and windows.