OK let me try
You said "My two cents.... or pence...... balance. almost any car, Ziggy's included, has front downforce due to the shape of the nose. That down-force has to be balanced on the rear to keep the car stable. Without that balance the car can, and probably will, spin at speed"
The shape of the nose does give downforce but it also gives drag. From previous post we know that the centre of pressure has to be behind the centre of gravity, like a dart to ensure stability, so Gary is correct that you need to add a wing at the back to counter the drag at the front to move the centre of pressure back behind the CofG but this is only one solution and not the best.
To move the CofP you can either have a large drag a short distance from the centre OR a small drag a large distance from the centre. The MOMENT of drag (drag x distance) has the same effect BUT a lower drag is always better so to counter the front nose down force it is always best to extend the body past the rear wheels and add fins far back.
It always best on a speed car to lower the drag as much as possible so also try to extend the nose out to lower the drag at the front. Nic gained 18mph with his car by extending the nose forward.
You said the following "While, theoretically, the car will be faster without wings, the reality is that it MAY be faster with wings to provide the downforce necessary to keep the tires glued to the ground. Without them you'll get wheelspin and actually be slower."
As stated above wings do provide downforce and traction required to accelerate and also at speed will increase the traction to overcome the frontal load due to drag. If you have too much power it is difficult to accelerate and so adding a wing to increase downforce will help but its not the best solution for ultimate top speed. IT IS the solution to getting the max speed within a limited run up!