I realize we really only have a twilight, rather than full dark conditions at night. However, I'd like to suggest some ideas for adding some of the flavor of night time operations. For instance, how about tying auto-gun engagement range to the light level, both against aircraft, boats, and GVs?
Regarding terrain, would love to see terrain type have an effect on GV speed. Sand, swamp/marsh, packed earth, snow/ice covered could all have some extra drag factor that would slow the max speed of a vehicle. Perhaps the magnitude of the affect could be tied to the type of conveyance, such that wheeled vehicles would be affected differently than tracked ones. Traveling on a road would negate the affect.