Welcome to the forum!

Click here for a similar thread about traveling the California coast. All of my recommendations apply to your trip (Madonna Inn, Nepenthe Restaurant, etc.)

Although I have been there, I don't have much in the way of advice for Vegas or the Hoover Dam, other than I think you'll enjoy both. Judging by the intinerary you have set up for yourselves, you seem interested in nature. Zion National Park and Bryce Canyon are two places that are less touristy than the Grand Canyon, but no less awesome by any stretch of the imagination. Zion and Bryce are also easy to get to and are no farther from Las Vegas than the Grand Canyon.

Make sure you eat at In and Out Burger while you're in California!