From a driver’s point of view the new Duetto was a big improvement over the previous 1965 Giulia Veloce Spider in terms of handling, comfort, soft top operation, and wind buffeting with the top down. A California car since new.
For more information on the design and development of the Series 1 spiders, please see: https://en.wikipedia.org/wiki/Alfa_Romeo_Spider.
In 1960 Pininfarina was asked by Alfa to design a spider based on the Sprint Speciale. This is what they developed in 1961 and what went into production in 1966.