Two nights each stop probably not enough!
but depends on how deep you want to enjoy each place.
In recent trip we spent 5 days in Death Valley and .... is not enough (we like to do hikes)! here is our trip:
Collection: Trip to West | 2013.
For us Vegas is not really attractive (didn't even go to the strip!) even this is our first time there... Valley of Fire and Red Rocks Canyon are two nearby LV places that are really worth visiting.
here is a good info about hiking around Las Vegas:
Bird and Hike . com
(I would advise to save the hike you want to do in PDF and put in your smart phone, many lesser known hike are not easy to find, and not everyone heard about them)
If you are into starwars.... check out their shooting locations in DV (star trek as well, in the area).
If you are into UFOs, check out the Extraterrestrial Hwy and the black mailbox (the road trip in the movie "Paul")... and.... Area 51!.
If you are into ghost cities/wacky stuff, plenty to explore in that area (crappy Flintstones park?).
If you are into road trip.... you can plan your trip around remaining portions of Route 66, and see those road trip stuff like neon lights, motel...