We were there last end of Feb to March 1st or so. Even then, it can get very hot during noontime. Stay on the known roads and do not just trust your GPS. DV is HUGE so even driving from Dante's View back out to say the lowest spot salt flat takes over an hour. So be sure to tank up frequently at either Furnace Creek or you can go out to Butte, NV, or carry extra tanks.
Zabriskie Point is a must see. Get there at least 30 mins before sunrise and the view is AWAY from the sunrise (I was wondering why everyone was pointing the cameras westward, ha ha). Aguereberry Point is great for sunrise also.
We don't have a off-road vehicle, so we didn't go to Racetrack, but really so much to see.... be sure to pick up your kaws from the floor ;-)