It could be that the outer cladding has finally worn away and that you're down to the base metal below it, which would then erode very quickly.
I replace the tips on a couple of my irons that are in frequent use every year or two.
On the temperature control issue, the fancy thermostatically regulated units are very nice, but for many years I had a very cheap and crude control consisting of wiring the hot supply line through a diode with a switch across it. When I wanted the iron to just "idle" for a while, flick the switch open and the power drops way down. It took only a few seconds to come back up to full temperature upon closing the switch again.
