That loop is up by heber/midway. We will be riding there with the family on Monday, it is pretty rocky but overall it's a fun ride. Not too challenging, but it can be moreso depending on how fast you want to ride.
The dunes will be fairly crowded this weekend, but I say go for it. I go every year on easter weekend which is the most crowded weekend of the year and it's really fun, you get to see all of the cool toys come out and play. There are about 80,000 people there on easter weekend, I'll bet that this weekend you only see about 30-40,000 max there. It will only be crowded around the sand mountain/white sands areas, once you get out into the dunes it is fine. I would rather go there than anywhere else probably.
Last Easter, no 250's (or 450's) beat me in drag racing. Only 2 500's managed to walk away from me. It must be my weight (150) because I can usually click 4th gear where others can only pull 3rd which gives me a big advantage.
-Richard