For Moab/Arches/Canyonlands - Consider Green River if winging it and having a hard time getting into a place. A bit more of a drive to the sights, but still a nice option.
In Green River the John Wesley Powell Museum is worth a couple of hours if looking for something air-conditioned, low key, and not crowded.
If traveling with dogs, the State Parks in Utah are more dog-friendly than National Parks - e.g. Dead Horse Point SP is right next to the Island in the Sky section of Canyonlands and dogs are allowed on hiking trails.
Have fun!
