Craig,
I was back at the Hoover Dam again yesterday, and I captured the following photo to illustrate what I was referring to in the post above:
See the black line near the lighter cylinder at the top of the dam?
The cylinder is the elevator that was built in the late 1990's to take visitors from the visitor center down to the Nevada Power Plant. It is basically a straight shot through sold rock and then visitors walk to a view platform to see the Nevada Power Plant and then back up the elevator. One never actually gets into the Hoover Dam on this tour.
The main tour goes down the historic elevator in the dam -- which is a lot more interesting and then over to the Nevada Powerplant.
So, to recap.
I don't think the "Power Plant Tour" is a good use of time on limited day for seeing stuff. If you could get the fuller tour, it would be worth it.
But you can see alot by doing the free stuff -- driving over the dam. Parking and seeing it from the Arizona side. Then driving back to the bridge viewing lot and then walking along the bridge from the Nevada side to the Arizona side. I captured the view of the dam (above) from the bridge walkway.
--> And you don't have to pre-purchase the Power Plant tour -- hoping for an upgrade. Just wait until you get there. If the main tour is available, you can purchase when you go through security. I wouldn't pre-pay the Power Plant Tour hoping for an upgrade--they are either available or they are not!
Mark