No convertible/Spider should ever have a tractor engine in it. In any case if you were to buy the diesel doing short trips all the time you would curse the day you bought it with all the associated issues the diesel cars have.
Sorry, thats not what you asked! Ensure full AR service history. At 50K the timing chain on the 2.2 may need changing, this should be considered a service item, not a failure. The chain on my Brera was changed at about 50K+ the Spider is at 65K and has not needed one, yet. The diesel will need a cam belt change but I think that comes at later miles. The only issue to plague the Spider is the hood, ensure it opens and closes properly several times without fault, I read on here many DIY attempts to fix hoods finish with frustration. We have had a couple of issues with ours, with the flappy motors, you'll understand what I mean when you see it operate. If you are anywhere near West Sussex, Kevin at Monza Sport understands the hood and keeps our perfect.
If you are looking for a street racer, the Spider is not the car. The 2.2 engine suits it well, sounds nice and makes for a comfortable cruiser and no diesel clatter. Short trips do not suit a diesel engine, but if you do decide that has to be the one, ensure it still has all the environmental kit (DPF etc) on it, it could be expensive replace it once the controls/MOT tighten up.