You can wait for them to start making noise before you replace them or you can just replace them while you are in there. They have a history of going bad and they have been in there 140K and by not changing them you are rolling the dice on whether or not they will make it to 210K. I would say the prudent thing to do is to spend the money on a new tensioner, tensioner pulley, and idler pulley. At that point the only thing left in there is the water pump, if it was me I would again spend the money and stuff in a new pump. I know that at this point it is getting spendy but I would rather have it all done right and tight and have the peace of mind that it is good to go.

Mark