After working a lot with electical(electrical engineer in a plant and a licensed builder), all the chared wires that I have come across that develop overtime are from a loose connection and not from the circuit being overloaded. I would change the breaker back to the correct size of 15 amps and replace the chared wires and outlets. I didn't have time to read all the posts, just scanned them, so there are no warrentees on my advice.
