I'm not sure why people are skipping the
"arriving in Vegas, staying for a few days and then driving to the south rim of the Grand Canyon, staying for one night and then spending a few days in Phoenix." part of my post.
I'm sure Denver, Utah and whatnot are just lovely this time of year but the itinerary is: a few days in Vegas, one night on the south rim, and a few days in Phoenix. The dates and destinations are not subject to change, so any further advice needs to be along those lines.

Oh, and did I mention that for the most part, we are NOT outdoorsy types?
@nbrindley, thanks for the advice - hopefully it's not too bad.
@heyyoucharlie and locofresh - I'm pretty sure one of my S.O.'s friends is taking us to Red Rock, so it's on the agenda

And yes, we are definitely fans of shopping!
@SnyderBock, while I'm not the biggest fan of Phoenix, I think Scottsdale is a nice area, particularly the downtown area and Biltmore. Also, I live one hour from Cedar Point - that's all the amusement park I need.
@combusean, I imagine we'll be at Amsterdams at some point so I can PM you my number. Sedona and Prescott sound nice, but that 2nd gear thing? We're renting a car and I do NOT do stick-shift!