If a shadow is good enough people don't notice it as a separate entity in its own right, so the fact that I completely missed it must mean that its certainly good enough for me

I don't think you really need to do too much more to the rocky coast.

As for the 'lack of detail' up top, I disagree with you there. If you look at other maps you will see that in most cases there are contrasting areas of detail and open expanse. Even an OS map is never completely covered all over with symbols (unless you are looking at a section of a large city, but even then there will be plazas and parkland). In designing something like this the open spaces are just as important as the dense city clusters of buildings