Should I or Shouldn't replace t-stat ???

Looking to do some general maintenance next month, plugs, oil change, clean carb, fuel filter, replace coolant...Its been about 10yrs since I put my Robert-Shaw t-stat in and was figuring on replacing that too since I'll be draining the coolant out. Do t-stat need periodic changing or "if it ain't broke, don't fix it" theory apply here fellas? I did notice lately that it may not be opening up to drop the temp like it used to. I never goes over 195/200 but usually the t-stat (180) will open up and drop to 180 regularly but not so lately. Maybe I just didn't pay attention to it before since it wasn't on the maintenance list.