I'm actually against removing the night-time speed. I just think it needs to be clarified (i.e, after 6pm to 6am or until visible light on the horizon fades/starts). As long as I see light on the horizon, I've always followed the daytime limit.
Maybe upping the night time limit to 70 on interstates, but on two-lane cattle roaming roads, 65 is plenty fast at night.
As for night time limits, Montana needs to do something, their car/truck split applies to the night speed (similar to how Texas signs most FM routes). If cars can go 65/60 (day/night), trucks go 60/55. Which, on a two-lane road backs up traffic and forces passing. At least Texas, at night, all traffic can go the same speed (65).