If these parts will be exposed to heat that is higher than the Tg of the resin without a post-cure, then you may see increased print-through and in extreme cases you might get discoloration of the resin and possibly distortion. In these cases it is always better to post-cure, though it's still possible to put the parts to use and they will post-cure naturally - the likely outcome being that you get a bit of print-through. 

Temperatures were in excess of 30°C for most of the day and I made sure it was in direct sunlight from morning 'til evening, so no doubt surface temps were a fair bit higher, although I didn't measure. 

Distortion is unlikely, especially on a curved object like a mudguard where the carbon is under tension, it tends to happen easier on flat panels. A curved object will be more likely to twist if it lacks fibre orientation at 45 degrees, but it will take some prolonged exposure to heat well above the Tg of the resin to occur if the part is free standing. If the part is twisted, then heated beyond its Tg, then allowed to cool in that position then this will likely result in distortion.