don't need a 4wd. just make sure you have good tires and a real spare. road is totally driveable in 2wd. it's just super washboard and the chert near uhebehe crater will puncher your tires if you drive fast.
I don't live in that area, I only visit 1-2 times a year via rental car from Las Vegas. I took one to the Darwin waterfalls one time and that was a rough road for 5 miles... I don't think I'd risk the longer journey to that Racetrack in it unless it was a different kind of vehicle.
Ok so here's my version as told to a friend who is a geologist:
I camped a bit south of the playa . ' was woken up in the middle of the night by some odd light and what sounded like a heavy bass track coming from a long way off, seemed to be coming from the playa, so I got up and started walking north hoping to find some hallucinogen crazed drum circle. As I got closer I noticed the pounding had stopped but the south end of the racetrack was lit up at places. I proceeded slowly and as I got closer I could see that pools of light were centered around the stones and contained a few figures dressed in what looked like white hazmat suits. I didn't want to get closer, things were a bit creepy, so I got out my 70-200 lens so I could see closer without being detected. What I saw was amazing. There were people out on the playa bent over the rocks with archeological tools dusting away the hardend silt and carving patterns in the playa floor. It was amazing, there must have been a hundred people out there sculpting the trails into the playa behind and around the stones. As the sun started to come up they gathered up their tools and their floodlights and started walking north. I, of course, followed them stealthily. As they approached the grandstand the rhythmic bass sound started again, and to my surprise the whole grandstand began to open up like a giant trap door. The people descended into it as through they were walking down a ramp. So, you see, I know how the rocks move. They don't. There is actually a colony of artists living under the grandstand ( probably some rejects from groom lake ) who come out every night and sculpt the trails behind the rocks so that it appears they are moving. It's all a hoax.
And here is their Sciency version:
Flash floods fill the playa with several inches of water, the water freezes and creates a solid plate of ice (winter conditions, obv.). Partial melting of the ice in concert with winds funneled down the canyon cause the ice plate to move, dragging the rocks along like bratty children on a slimy surface of salty clay. The surface area of the ice plate is considerable, so it doesn't take much wind to push it along. Eventually, the ice melts and the water evaporates, and all that remains are the dirty old rocks and their filthy skid marks.
Personally I think if you think mines true you've got serious head problems, but if you'd rather her's were true instead of mine your boring.