Has anyone got any thoughts on the Grand Canyon 'day trip' as I mentioned before?
Yeah. I'm thinking "Wish I could do that". I haven't but it must be plausible because tour companies do it regularly on a bus. Here's one, as an example not an endorsement, that says it's a 14 hour trip with 3 hours at the canyon plus stops at the dam and in Kingman. You might think you could do it faster in a car but don't count on it. You'll find different places to stop, etc., and you won't have a rigid schedule to keep you moving. You may even want to consider a bus tour to eliminate some planning and allow some sleep on the expressway run back (I assume) to Las Vegas. But, if you chose to drive (and I think you should;-) you'll also be able to experience one of the better remaining strips of Historic Route 66. Yeah, the bus tour description says it does "Travel along historic Route 66" but...
The hundred mile stretch between Kingman and Ash Fork is the longest unbroken piece of the historic road that's left. It includes Hackberry General Store, Seligman, and plenty of lesser known cool spots. There is no single "best part of 66" but this section is a legitimate candidate. DeLorme says it's a three hour drive and you'll want to allow for a "half-off cone" at the Snow Cap and a couple of other stops. I-40 covers the same distance in an hour and a half. Do Sixty-Six one way and I-40 the other. One direction or the other is almost certain to be in the dark. Make sure it's the I-40 bit.
My one visit to the Grand Canyon was about three hours and, no, it isn't "enough". I mean it isn't enough to say you've seen it all but that would take infinity plus or minus an hour. It is enough to be incredibly impressed.
This year, you will be able to drive across the Hoover Dam and, as far as I know, stop on top of it. Next year, traffic will travel over a separate bridge currently under construction. My first view of the dam was driving north from Kingman at night. As an ignorant young (well, younger) man, I didn't even know we were anywhere near Hoover Dam. When the lighted towers appeared around a curve, I thought I was approaching the witch's castle from the Wizard of Oz. You'll get to experience that -- minus the ignorant part.