Be sure you get something to eat by Barstow. No much at all between there and Vegas, but IN Vegas may I suggest you get that steak at "Mon Ami Gabi" in Paris Las Vegas? Don't eat outside, as you will wait an hour for a table there and then have passers-by blow cigarette smoke into your faces. Inside is cool and infinitely quieter. They bill themselves as a "French steakhouse," but everything else we had was great. Ask what they can substitute for the steak frites, which are long on presentation and short on taste, and do ask for Stormy the waitress. Never tried the places you mentioned, but wasn't there a Palms steakhouse in Chicago that got laughed outta town?
St. George, Utah has all kinds of chains near the freeway (I-15), but go into town on St. George Boulevard west to Ancestor Square. The Painted Pony is suposedly the best restaurant in town, but we found it inconsistent, The Chinese restaurant downstairs is delicious and thrifty. Have dessert at Nielson's Frozen Custard, and avoid Iceberg, which was inedible. St. George is a good base for the North Rim, but I hope you also see Bryce and Zion canyons. Visit the NPS websites for all these parks to learn about "The Grand Staircase" that starts at Cedar Breaks above Bryce and culminates in the Grand. We enjoyed lunch in the dining room at the North Rim, but the dinner we had at the South Rim's El Tovar Dining Room was even better. Call for reservations there NOW, and follow their instructions for calling back the day before if they say they're booked.
The area of Utah and Arizona you pass between St. George, the North Rim and the South Rim is some of the most sparsely settled land in America, so make sure you have plenty, and I mean PLENTY of water and beverages, as well as snacks. Buy groceries--and water--at Smith's in St. George BEFORE you buy gas so you get a discount on what is already the lowest price in town. Gas in those little towns is much higher.
You must pass through police checkpoints before you drive across Hoover Dam, and tours of the generator plants seem to be allowed for some but not others, and on no rational basis. The total experience is like going through airport security again and again, and left a bad taste in my mouth.