I only wipe mine (with kitchen towel and warm water) if they have definite chicken poo on them, otherwise so far as I gather from my research it is better to leave them. The shells are naturally protective and anti-bacterial until they are washed when their coating is then removed. Also there is a risk, as birdsrfun has said, of actually transferring disease into the shell because the shell is porous.
One of my hens has a tendency to lay in the roost in the midst of the night's droppings... I know who the bad girl is as they all lay different coloured eggs... >:( ... those eggs are really filthy mucky so do I wash them, keep in the fridge, and use quickly for fully cooked dishes.
My sister, however, who has been keeping hens for 30 years, always washes hers because they look nicer. Her chickens are properly free-range and have very muddy feet and odd laying habits ;D She has never, so far as we know, had any egg related problems.
So perhaps it is a matter of preference...