Not sure what gas mileage you were expecting but from what I’ve read, most owners are getting between 14-19 in city driving; 22-25 in highway driving. At one point, we were getting about 14-15 city driving. That was with a ton of short trips and never getting over 35 mph. Now that my wife is working more, our city mpg is just over 18 mpg.
With regard to the passenger visor, I would check how easy it is to remove and change it. Many Nissan dealership sell parts online and are often cheaper than walking into your local dealership to buy parts.