... My only niggle is that the elements are relatively bright considering that they are back-lighted...
In addition, there are three other related issues: contrast, saturation, and white balance of back-lighted or shaded areas. Contrast and saturation tend to be less pronounced there. White balance also differs. This applies regardless of whether one is using a gradual ND filter or manual blending in post processing. There is a standard "shade" white balance in most processors for a reason.
What it means for your image, Enda, is that I would lower the contrast and saturation a bit and then experiment with a different white balance for the shaded area. When it comes to the sky, I kind of dislike that muddy orange you got (probably a result of the ND filter) and would also try to play with different hue and saturation levels for orange.
Back to playing with the shaded area. When experimenting with different WB settings, I would try two distinct approaches: one would be the "shade" WB, in which case it would kind of blend in with the overall warm feeling of the sunset. The other approach, in general, though not sure if specifically for this image, would be to accentuate the contrast between the warmth of the sunset and the coldness/bluishness of the shade by making the shade even more blue.