With regards to the Roadster, Tesla's major value add was the controls. ACP was using Analog controls, Tesla ditched these controls and created their own digital controls. Tesla Roadster technology is loosely based on ACP, but ACP's manufacturing process was not suitable for mass production so Tesla took the best of ACP, created better process', better quality and less costly materials and turned it into a marketable scalable vehicle. Even today the digital control algorithms that Tesla patented for AC excitation motors is the main reason behind the performance advantage of their vehicles.
The story goes that Martin Eberhard paid Alan Cocconi the full price of a T-Zero up front but ACP was unable to deliver the car and they refunded Martin. This money was then used to bootstrap Tesla Motors. I truly believe that if ACP delivered that T-Zero, Tesla Motors would not exist.