06 Sienna at 230k miles with original Iridium spark plug.

It is recommended for replacement at 120k miles in the manual. I did not change it for two reasons: 1. there is no signaficant drop in gas efficiency. 2. It is time consuming for replacing spark plugs in 06 Sienna (the back three spark plugs). I did open one of the cyclinder, the spark plug looked normal at 160k miles or so.