For me, Vegas is a place to eat, get gas, and LEAVE! I'll echo the recommendations for Zion and Bryce. From there, you can continue northeast through Escalante and Capitol Reef - not quite as spectacular as Zion and Bryce, but much more enjoyable riding as you'll leave most of the crowds behind. You can also get to the Grand Canyon from there. Same canyon but the much less crowded north rim! If you are looking for others to ride with, post something on Advrider.com in the West regional forum as locals often set up rides there.
BTW, Vegas is HOT - 42* C today.