on the bright side, that weight penalty can be located very very low. That doesn't help with acceleration but improves braking and cornering performance.
A Lotus Exige already has near perfect weight distribution and low center of gravity. Since it is mid-engined it also has 160KG of engine over the rear axle which improves traction.
Adding an extra 500KG and putting it lower in the vehicle will not improve braking performance, handling or agility.