Are you going there for the Moab Off-Roadeo? Lucky you!
However long you're there, it won't be enough. I gather you're not going there with your own Bronco, but will rent a vehicle in Colorado and drive there? If at all possible, rent a Wrangler, spend the money. I reserved one in Salt Lake, and when Enterprise couldn't produce it upon arrival, I had them call all over until they located one, and it made a big difference. (I needed to hit backroads to research a book.) That Wrangler, probably a stock "Sport" model, will still let you explore lots of fascinating and scenic trails. And having done the Off-Roadeo, you'll have a feel for trail driving. Check this out, very detailed with accurate trail ratings.:
I'll leave Colorado recommendations to others. Moab will be worth whatever time and money you can indulge. So indulge!