I think for the image I'm just beginning on, the mirror approach will work well. I won't need a displacement, since the water prop already has a morphing geometry. However, I would like to know how to handle both cases. I'm going to guess that it will look a bit like your open water shader (which uses both reflect and refraction rather than fresnel so it handles non-clear water.)

When I manage to get my first attempt done, I'll post it.
Isn't specularity also affected underwater?