We like to schedule 3 nights in a park which gives us 2 full days to explore but we don't get to hike much because of our dogs. There have been numerous times that we wished we could have stayed longer but with 2 days, you can see a lot. We know where we want to spend more time now!
Check out Dead Horse Point & Goblin State Parks as well. Dead Horse Point has a nice campground and is near Canyonlands and not far from Arches. Goblin is worth the side trip to get to it.