I did a Hoover dam tour like 25 years ago. The guide was so stupid: When someone interrupted him with a question, he had to start over with his speech for the current site from the beginning. He had just memorized everything (and somewhat poorly) and could not talk freely.

Not telling this anecdote to be mean. It's just of the memories that stuck from my first visit to the Western United States as a child.

Edit: But yeah, the visit to Hoover Dam was worthwhile other than that. Haven't been since, though. On more recent trips, we enjoyed the state/national parks near Vegas. Some are quite close and can easily be done as a day trip.