The creator has stated that he does not want his story to have romance as he believes young boys do not like those kind of stuff. So to put it bluntly, no they do not kiss.
well nami and luffy never kissed so but the creator of one piece oda would like to add romance at the end of one piece when luffy becomes the pirate king nami will love him and not just because his berries cause she loves him >.<
No, both Sanji and Nami have never kissed in either the anime or the manga.