Well, over a short period, PCP may
seem more expensive but this is because you are also building up a deposit to put down on your next PCP deal. Most PCP companies try to make sure that their GFV is about 20% less than what they really expect the value of the car to be.
PCP also gives you the option to spec your very own car so you can choose all the funky extras you'll definitely need in a convertible! And you won't get bored of a mini convertible - not even in 10 years

It's a no brainer for me.
Given that the new hatch comes late 2006, the new convertible will take
at least another year to arrive. Even given that though, I'd shy away from being a guinnea-pig for a new model - I'd wait until they've solved the initial issues with the car, especially given your need for good quality.
The same argument goes for Golf convertibles, but you also have to remember that they are also
blurry ugly - don't do it!!