Two points jump out at me:
During a self defense shooting situation, relaxation is next to impossible, and
In all of the self defense shootings that I know of, the subconscious appeared to be in control of the actual act of pulling the trigger. That is, some people remembered seeing the front sight, others only remember seeing the threat, some remember the recoil of their pistol, others don't...but none of them remembered pulling the trigger.
Would techniques of visualization be useful in combat shooting? Of course. Any training that results in rounds going where you wanted them to is fed into that wonderful combat computer God stuck between your ears.