Ok, here's what I would do with the reasons why.
Day 1: Fly in to Vegas. Plan a nice dinner & a show.
Day 2: Morning, go see Hoover Dam. Afternoon/evening, tour the various over-the-top Vegas hotels, this is quite a bit of walking unless you just pick a few that are in close proximity. Head down to the Fremont Street experience after dark.
Day 3: Get an early start and drive to Grand Canyon, planning your day such that you arrive by early afternoon. Visit as much as the Canyon as you can in the afternoon. Plan on dinner after dark, so that you maximize your daylight hours in the park. Overnight in GC NP.
Day 4: Get an early start, see more of the GC, leaving 11am. Arrive Sedona by mid-afternoon, this drive is beautiful, be sure to do it during daylight. Take the 180 to 89a and drive through Oak Creek Canyon. In Sedona, take a Pink Jeep tour that starts late enough in the day that you will be on the tour around sunset. Ideally stay O/N in Sedona (surely there is a Marriott there), if not, drive down to Scottsdale that night.
Days 5, 6, 7, & 8: Relax at the Westin Kierland, being sure to go get yourself a Toffee Banofi sundae, and flying home on Day 8.
H