When telling friends I was visiting the Hoover Dam, I got much of the same response. Laughter. It has seemingly become lame to be American and visit great American tourist attractions. In fact, we noticed that most of the tourists were foreign (including a huge German biker gang) and loving this engineering wonder on your home turf. You have no problem seeing the Eiffel Tower or Leaning Tower of Pisa, right? So visit Hoover Dam (it!)!
The Dam was constructed from 1931 - 1935 and ultimately helped contribute to something near and dear to my heart...the ability to get provide power to great cities like LA. The project was a huge undertaking without which, there may be a little less light in the West.
We went for the $11 tour vs. the $8 entry to just the visitors center. You may as well pay the $3 extra to check out the massive pipes and other crazy contraptions that make this thing go.
Consider taking a day trip from Vegas and see what makes The Strip light up so beautifully at night!