All comes down to cost I guess. I'm no fan of BMW as s rule, but felt they produced a good product with the Z4.
I felt the Audi cabriolet and A4 convertible would be real contenders due to price, drivetrain choices and quality. Cabriolets were never a particularly pretty car IMHO so I was thinking they could be a donor with very wide appeal.
But back to the Z4 - the better the bar - the fewer surprises. I just thought they were quite different in length than the Daytona's wheelbase but can't fault the 360/430 outcome so it will be a wonderful journey!