Sorry not to see your message until now, Joel. 

I also understand that the mean highest high tide line is the best one to use for the coastline. 

That said, I do think there is generally some beach between this line and where the terrestrial plants start, and if there are too many overlapping features they obscure each other in many renderings. I don't think we can say with total accuracy from the imagery where the mean spring high-water line is, so spreading the coastline and the highest point of beach may or may not be technically accurate, but allows users to see the info better.  Many renderings make the fact that there is a beach impossible to see, if it is entirely below the coast line. 

I think it is more useful to take my approach, to keep things clear, and I hope my approach is ok.