How much will your insurance premium go up if you hit the car of a visitor parked in the driveway and only the visitor's car was damaged?

The answer depends on a lot of factors, but you probably don't have to worry too much. Who your policy issuer is makes a difference, because some companies are simply better than others. Your driving history matters, too. If you have a history of crashes, your premium is more likely to go up. If, however, you're considered a safe driver, even if your policy does go up they may counteract it with an equal safe driver discount. But since the collision involved a non-moving fender-bender, there's probably litte chance your premium will rise too much if at all.