In the field not all Soldiers get expensive NVG's. I remember from my own experiences with LUCE Night sights they were expensive and every other or third man had them. Whole units having them was rare.
Therefore alot of training was given to the "MARK ONE EYEBALL" and how you would improve your Natural night vision (Not just by eating carrots!).
Night Vision improves not only with time as your eyes adjust but also with knowledge of how your eyes actually see (Rods and Cones and their location and relative density in the Eye).
Equally protecting your Night Vision with Red light and tactical use of light.
So I would like to see a system, where for every minute or two you are in the Dark, your visual range, or maybe the contrast improves by say a level. So after 10mins you have had 5 incremental improvements to your night vision. Maxing out at say 10mins, any firing of weapons, artillery explosions, or any bright light will instantly reduce your Natural night vision by say 2 increments. A flashbang by maybe 5 increments.
Equally shifting from NVG's to natural vision shopuld incur a massive penalty as your eyes have to adjust massively from the Photon's in the NVG, to the lack of them with Ambient light.
This is to try and simulate the whole Tactical Night Vision, rather than the lets all wear NVG's.