It's only worth pairing on complex code, rote code yields no advantage.
I think there is a point to this - pairing is about improving design and minimizing mistakes. Rote code that's simple to write yields little opportunities for pairing to make a difference.
Except this: writing boring rote code is a smell. If I'm writing boring repetitive code it's usually a sign that I've missed an important abstraction, one that will drastically reduce the amount of rote code to write. Pairing will help you find that abstraction.