I know we're not specifically talking about the S2 Spiders here, but back in 2011 at our AROC national convention here, I was very impressed by the performance of an S2 during the autocross. It was a virtually stock SPICA Spider, vintage '72 or '73, so it did not suffer from added weight of impact bumpers and was in excellent condition mechanically. Alloy wheels, Toyo or Falken tires, but best of all an owner and driver who knew the car and knew how to push it to 11/10ths. That Spider was dancing in perfect response to steering inputs, well balanced with really good power and torque on display! It was a performance sight to behold, and would have muted many a critic of the "antiquated" Alfa chassis design of the day. There was no way in the world my tweaked S4 came close to his times that day.
IMO the S2 is the purest, most visceral example of the 105/115 Spider series.