coming into this a bit late, but I offer this:
I've shot at DV the past 5 years, and work the dunes a lot.
Location wise: My (car) GPS has N 36.60482 x W 117.13067 as a spot along the road which is close to what I think is the easiest/best access to the dunes - as others have stated, this is not the parking lot / typical tourist entry point to the dunes, but rather a spot off the road in between stovepipe wells village and said parking lot - it's a LOT easier to head into the dunes from this approach than it is from the lot. It's still a 20+ minute walk to the dunes though.
That being said, every time I go, I choose a slightly different entry point and approach angle as the compositions are quite varied.
Good luck, great place to shoot.
Just a quick reply to thank you for this info. I was there this morning at 6.45am, about 25 mins before the celestial sunrise (the sun comes up 5 mins or so later behind the mountains). The hike is indeed about 20 mins. I was alone, but there were probably a dozen or so photographers at the park-designated trails that originate from the parking spot. (Thought that was a huge number for a weekday in October.) The light is definitely magical, and absolutely worth the early start of the day.
Here is an initial image. D7K, new 50mm 1.8, HDR in Photomatix.