I think the added breaths look very good and are well-executed, but I'm not sure it would really be that cold inside Echo base. I know 3PO says it's supposed to be freezing in the Princess' chamber, but a lot of characters are walking around with no head-warming protection, and their skin colours betray the actual ambient temperature of the set (if it were so cold as to see their breath, then I'd expect their noses and ears to be red as well).

Ultimately I'm on the fence -- I'd be fine with or without their addition to the film.