The stored rotational inertia is proportional to the square of the wheel's rpm, and proportional to the moment of inertia (derived from the static weight and shape). So it is significant at high speeds. Expensive wheels may not ultimately pay for mpg decrease, but may win a race.
When you go to a ++ size like 17" or 18" the low profile tires that fit these wheels have higher speed ratings so they weigh more than the factory tires. You have to weigh the tire/wheel package to make a valid weight comparison. Factory wheels are very aerodynamic with the trim ring. Most any aftermarket wheel is not as aerodynamic. You will be lucky if you break even on mileage when you make a tire/wheel change from stock. Also an FYI. The 16" factory Touring wheels are magnesium, not aluminum
you may notice the acceleration also the bigger wheels mean bigger tyres and more mass further out ( means faster when moving) also don't forget tyre speed ratings the higher the speed rating the more heavy steel in the beads to retain the tyre on rims should a slide happen. I always get H rated tyres for the Prius