Breathing techniques are not the same as how much oxygen one gets; breathing slowly and deeply calms the body in and of itself and is good for anxiety and stress situations.

Oxygen saturation of the blood is measured whenever there is a breathing problem (I have asthma, for example) or one goes to the hospital for a problem, it's a measurement like taking one's blood pressure and is a "standard" measure. It is estimated that 80% of the population has deviation http://www.obstructednose.com/nasal_...on_septum.html and yet there is no difference in oxygen saturation (my nose was broken December 2010 AND I have asthma) or mental health from those without. I don't think 80% of the population has mental problems that could be helped by getting their deviation fixed.

If you have difficulty breathing, nose bleeds too often, sinus problems, I would get the operation so you do not have those problems. It will probably not help any mental problems unless you don't like how you look or maybe if you believe problems are related to air flow in some way, as you seem to.