What's the weight of one of your old wheels, if you don't mind me asking? I might be interested in taking them off your hands.
Rotating mass is a funny bugger, but as a rule of thumb every 1kg you take out of a wheel is about 4kg of unsprung weight per corner removed from the car. This means quicker reactions from the suspension, accelerating, braking and steering response. You want the smallest and lightest wheels you can get for the track.
As Woody mentioned, a bit of a length to go to if it doesn't mean winning or losing a race, but something to consider.