It's less than an hour from Vegas so if you want to do something edumacational during the day, I think an outing to the the Hoover Dam is worth it. Parking is $7 and admission is like $11 (I think) and they have discounts for military, senior and students.
The tour is great. The guides make a great effort in teaching you about the history of the dam without making it boring or anything. The movie at the beginning of the tour is cool and you'll learn a lot of about the dam. But doing the paid tour is a must since you can actually see the gigantic generators that converts the high velocity water stream coming in and converting it into electric power; and realize that this was 1930s technology that did it and is continuing on today. And you're surrounded by millions of tons of concrete that protect you from that high velocity water stream.
You can still do the "free tour." Basically just hang on top of the dam itself. Take pictures, walk across the dam too and go from one time zone to the next, but it's only $11 for the tour, so just do it. Plus, it's air conditioned so you don't have to worry about that desert heat.