When we went to LS, we didn't go through Nephi. It kinda seemed a little out of the way. Jackster got to check it out though.
Going north, Delta is the last place to fill up other than a small gas station/ market on the 6. I don't remember what town it is in though. Maybe Lynndyl. Delta has some places to eat, a couple gas stations, and I wanna say I even saw a Yamaha dealer just on the outside of town heading north.
The elevation isn't too power robbing up there. You shouldn't even have to change jets. I never did and had no problems.
There are a couple spots to get up and over sand mountain, but the I love the trails leading around it to the back where the dunes are. The trails are a blast.
White sands is a huge area to check out, but gets pretty boring as the dunes arent very easy flowing like Dumont. They are really small and hard to read during the middle of the day. They are easily white washed since they are, well....white. lol
Their vendor row is pretty nonexistant up there compared to Dumont or Glamis. lol It's small but theres a couple vendors that sell food, ice, and whatever. Not sure if they will be there on an off weekend though.
There is fresh water spickets throughout the camp area at sand mountain. As for dump stations, there are some at the white sands and jericho campgrounds a little farther up the road.