SINNO12,
My house is timberframe, built around 1996.
I'm curently refurbing the bathroom, and there's no insulation in the internal walls. However, I am putting insulation in when I am boarding the walls back up. The bathroom is situated over the stairwell/downstairs hallway, and can feel cold some mornings. Having said that, the rest of the house is generally easy to heat. It might be worth doing if only to add a little more sound insulation from noise.
teddyk.