The four planes are: Dark Plane (think shadows, darkness, imprisonment, exiles), Astral Plane (think gods, cosmic entities and heavenly structures), Arcane Plane (think anything and everything magic related), and the plane that Earth resides in. The last plane is unnamed, but it would look very similar to how our Earth or other similar planets could look at whatever point of time.
I think every plane could be representative of a feature in the game— Arcane plane for spells, items, powers, etc. Astral plane for weather conditions, revival, spirits, etc. Dark plane would consume the land at night, and the one of Earth will control the day. Dusk would probably be more of an earth than dark plane.
During the night, cloaked air units could fly across the sky to create a creepy effect, it may also make heroes more paranoid about cloaked heroes. Spawns may be more vicious at night, or a special type of spawn roams around (not attacking bases) like a powerful ultralisk (perhaps could drop good items).
For another terrain changing effect, the plyon aura could be placed to represent water. During the day, a waterfall, or stream could pass through this (bunch of hallu deaths) and units won't be able to enter these harsh waters, at dusk, the hallu deaths lessen, and maybe a use cloaked units or disabled floor traps cause some flow, you may cross the water, but you are pushes in the direction of the flow, and struggle to make it across, but at night, the water clams down and you may cross with no problem, there may even be a secret path or item under where the waterfall was. When you enter or exit the water a hallu death 'splash' shows. If you are pushed to the side of the water, or are in it when it turns day, you are flushed onto land.
None.