It looks like you guys have not only gotten around quite nicely on your own, but also identified your next destination: the North Rim of the Grand Canyon.
As you say, it's closer to Las Vegas than the South Rim, but not much closer; the South Rim is 278 miles, while the North Rim is 270 miles. Accessing the South Rim takes a little less time, because the roads (US93, Interstate 40, and AZ 64) are faster, but only by a half-hour or so.
Your trip to the North Rim starts out fast enough on Interstate 15 through St. George, UT, but from Hurricane, UT, to Fredonia, AZ, Rte. 59/389 is dinky, and from Fredonia to the North Rim, Rte. 89/67 is pretty remote. But to us, that’s part of the fun of the drive; you’re in some pretty wild country between St. George and the Canyon. Getting to the North Rim feels like quite an accomplishment.
And once you arrive, you’re in for a major treat. First, being so remote, the crowds are sparse, especially compared to the circusy South Rim. Also, because the North Rim gets more precipitation than the South, its walls are more eroded and sloping, making it easier to see the Colorado River.
There’s only one lodging and dining facility, the Grand Canyon Lodge at the North Rim. It’s extremely rustic, with '50s-style motel rooms and cabins, and has only one restaurant, with prices typical for remote national parks with no competition. It's staffed mostly by young seasonal workers who work the national-park circuit (the North Rim is closed mid-October through mid-May). So if you’re looking for Ritz quality and Vegas prices, you’ll be in for a shock. But it doesn’t sound like you are, since you’ve been to Death Valley and Zion/Bryce and crave the outdoors.
Still, it's good to be prepared for the North Rim. If you can, stop off at a supermarket on the way and stock up a little with snacks and supplies; otherwise, you'll be captive to the limited offerings and high tariffs. On the other hand, you definitely want to plan to eat at least one meal in the Lodge dining room, which is right on the rim with a spectacular overlook of the Canyon, especially at sunset. Views from the hotel rooms, as well, are stunning; from the porches of the four cabins, you can see right into the canyon.
Beyond the facilities, the North Rim, to us and many others, has wilder and more spectacular scenery than the South and better hiking trails. The views are clear, not so hazy. The most accessible overlook is Bright Angel Point, an easy half-mile round-trip stroll from the Lodge. The scenic drive is 23 miles one way to Cape Royal. Along the road, stop at Point Imperial, the highest viewpoint at either rim. Farther along are vistas at Encantadora, Roosevelt Point, and Walhalla. At the end of the road, stretch your legs on a half-mile walk to Cape Royal for an unparalleled panorama.
By the way, for anyone interested in some serious hiking in the Southwest and California (including the epic two-day South Rim to North Rim to South Rim trek), we're just about to release two hiking guides, Hiking the Southwest and Hiking the High Sierra, by our own inveterate Branch Whitney. The print editions of the new titles aren't due back from the printer until early next month, but you can download the e-Book versions now (no special reader required).
Finally, if you're making a ten-hour round-trip to the North Rim this time, your next journey might be a similar-length trip up the east side of Nevada to Ely and Great Basin National Park. For a description, see QoD 2/3/06.