Agree with everyone on this topic so far. OP your friend sounds like an idiot and is probably jealous of your new car. Think to yourself what would be the best place to put your money in your new car. If you feel a wheel upgrade is top priority go for it. Any and every car can look better with aftermarket wheels. The 5 spoke Si wheels you got look awesome and will probably make your car look even better.
Expensive rims aren't always light, so that means their not just for racers. There's a lot of factors that go into why the rims is the price it is.
And light rims aren't just for racers either. Lighter car=better gas mileage.