Two facts about the Hoover Dam--first everyone should see it; second, the tour gets dull in a hurry. There is a better way to see this modern miracle that reshaped the desert southwest, and it's by kayak.
Operating out of Boulder Colorado, Desert Adventures offers an inexpensive and pretty incredible trip out on Lake Mead on Kayak. They drop you off on the lake, and the water, unlike the Great Lakes of the Midwest, is bath-water warm. They actually warn you, "The water is very warm, so bring some cool drinks."
Wow, coming from Chicago that's a unique and wonderful thing to hear.
This will be a better trip if at least one of your party is in pretty good shape, and can tow the rest of you when they reach the point of exhaustion. The water is glassy and calm, so it's not a rugged trip, but there is a lot of the lake to explore, and it's very beautiful.
It'll take about an hour to move the kayak to the point that you can see the dam. Even better, there are some small islands on Lake Mead where you can dock to picnic, swim, sunbathe, hike, explore some small caves, etc. These tiny islands are inaccessible other than by watercraft.
It's truly a unique and inexpensive afternoon, and something in the hot dessert outside Las Vegas that nobody who like boating and the outdoors halfway should miss on their next trip to the casinos and shows. In fact, I say go to Vegas for the kayak trip, and then enjoy a little gambling and a cocktail after you get back to your hotel.