Perhaps a better question would be "Are people without a vivid imagination ... sane?" The implication of the original question is basically that no sane person really imagines very much-and certainly not very vividly! So is the person who can create his or her own "reality", either just in the head or on paper, alone or with others, really "crazy"? The answer is a resounding NO!
Watch children playing. Most of them, when they aren't watching television or playing computer games, will be playing. Our grandsons love to play cops and robbers. They also love to "build" things, and have tried hard to make their own playhouse. The granddaughters also love to play, sometimes with the boys in their games, and sometimes separate from the boys. They may pretend to be rock stars or homemakers, or even teachers, bosses, or any of a plethora of other occupations. And in their pretend play, they vividly imagine themselves as being exactly what they are pretending to be, just as I did when I was their ages. Every child who is considered "normal" goes through the process; one who doesn't is thought to be "different" and therefore someone to avoid.
And what about writers and artists? Writers have to create their own characters, locations, weather conditions, etc. And they have to make sure they are at least believable. If not, their writings won't "sell" to the intended audiences. Artists create their works of art, sometimes from their imaginations. And if they have imagined a beautiful scene, they create a beautiful scene. If they imagine a horror of some kind, they create that horror so the viewer can actually see and feel the horror! This ability to depict, realistically, the things that only existed in their minds before-does it mean the artist is crazy? Or does it mean the artist is gifted and really talented? Most of us would quickly agree that the latter is the answer.
We need to remember, too, that a lot of the things that we take for granted were once the products of someone's imagination. For instance, the Eiffel Tower was once only a dream; however, it has stood for hundreds of years simply because the person who "imagined" it was gifted enough to at least draw the plans for it. The Taj Mahal was once a product of someone's imagination, yet it has been visited by millions since it was designed and erected. Was the person who imagined it "crazy"?
And think about all the equipment and other things we use every day! An electric or gas stove, televisions, computers, tractors, mowers, vehicles of all kinds - the list could go on and on and on! These all were once the result of someone's vivid imagination; and they are now an accepted part of our daily lives!
No, people with vivid imaginations are NOT crazy! In fact, the opposite may well be true, that they are really the sane ones, and everyone who DOESN'T imagine IS crazy!