There is a compromise between adding a space and not adding a space which I have not seen in @jancborchardt’s awesome list above: Add a space and place the cursor behind it, but watch what the user types next: If it is punctuation, silently remove the space. If the user types a single space, simply ignore it, assuming the user did not notice that the space was already there.
This is the behavior that is implemented by iOS when a word from the predictive typing suggestions is selected.