DO IT LOL ..
T5 is a great engine, cool roof mechanism. Bargain convertible compared to E class etc. As you might be able to tell its a marmite car. I love 'em.
2013 model well sorted, so probably best of the range. Styling less aggressive than early models but that was Volvo's market at the time.
As for buying a convertible, I would say do it if the roof coming off is the most important feature of the car. If not, get a saloon and a sunroof! There certainly are compromises you have to live with in a C70 (rattles definitely being one of them!).
Keep the roof and seals well maintained, door locks lubricated, gearbox oil changed and the mechanicals are very reliable. Dampers work hard, so might need changing at 90K onwards.