You’re welcome, Jerome.
Water is a tricky material, as it is invisible and lives only based on refraction and light, except when it is contaminated ;o)
So, the specular highlights are certainly an indicator for water, but an HDRI based reflection might be better. Why? Because the light in the HDRimage would anchor the drops more in the world. The Specular highlights are without (real world) effect natively in CG, as a bright light-source that would cause such an effect (specular), would result in caustics, which is as well a render intensive effect. If you can render the drops as alpha mask (in color correction terms, “qualifiers”), you can adjust the brightness a little bit behind the drops, to increase the effect on the “wall”.
However, if you can move the camera dynamically, it might help a lot, to sell any change in the lights, as movement causes similar changes anyway.
Motion blur in post. Well, it is more common than not for 3D render. But post means, you apply something to a single pixel, not layers of material anymore. (Deep Compositing is not available in Ae). Having said that, I like to experiment when time is precious, to separate the background (wall) from the drops (foreground, in a way), at least the specular highlights might be better “motion blurred in a separate pass, and then brought back. What I did in “JET” was to render in SubFrame Motion blur to a small degree, and use then a Motion Pass for Ae, which is not precise nor correct but closer for multilayer materials. Automatic post motion blur is not to my liking, it simplifies too much, but—yes—people get used to this fake as they do got used to fake explosions in space (no one has seen a real one ever, so we believe in a VFX reality).
I talk about this since a decade and I hope that the 4K (UHD) will set the bar a little bit higher, so the results will improve, as it has from SD to HD. However, effective editing and avoiding long single takes will help here of of course.
My best wishes for project
Sassi