Waste of money. What possible performance could it add? I think ones like Mugen are windtunnel tested and thats why they cost $1000+ for a kit. Most other body kits will slow your car down since it adds more drag and then the kids in the back of the station wagon will point and laugh at your pos.
So are you saying that a mugen body kit will help or hurt your performance? Also, if bodykits hurt your performance will it be a dramatic change