Correct on if you block of engine bay air from being taken in by airfilter, then the cooler outside air will help richen the AFR up and also help IAT to report cooler airflow.
How much gain you get just with the cold air box will depend on how lean LTFT was and how much cooler the airflow andIAT are with box on.

As for doing the injectors, with the cold air box and either using a MAFT or new PCM calibration, in my case as I mentioned HO went from 435 to 500 HP at flywheel but I worked hard in tuning everything in so functions all worked well together.
Anytime you can reduce injector on time is less load on PCM clock time and amount of current being sucked up from injectors and coils being on.