The used car should have all the bugs worked out by the previous owner (in theory) and you could go with the extended warranty. I always thought i should have gotten a convertable, but I do like the open air.. My first one was a 2008 Pure and I couldn't be happier with it. I now have a 2009 Pure, same exact model, and I love it too.
Have not heard anything on top leakage on cabrios, you can always add seat covers to take care of the seat stain.