I've really liked the coupe version since I first saw it, but having a convertible would be awesome for summer days. My folks have two convertibles (saab 93 and Audi tt) and with the roof up, motorway noise is fine, but even with the wind breakers I'm not sure I could put up with it for a very long while down the motorway - it does tend to get to you after a while.
Down the fun roads and even normal single carriageway roads it's great, but with the extra noise (and things like lorry smog, and any dust that gets kicked up {especially through roadworks etc} as you pass them) you'll probably end up with the roof up for large amounts of your journey
Tl;dr convertible would be awesome for when you get to use it, don't think you'll end up using it too much on the motorway