I still think the paint effect of the white water would be necessary but the clear resin would just give it that depth and that slight bit of translucency to just put the piece over the top....but as we know clear resin is very delicate and more expensive so i can't imagine what this would have cost if they had gone with it.
If you look at the old Sideshow Namor Vs Iron Man diorama, a water effect like that would have been fab!
But yes like you, i still think this a brilliant piece and the much lower price point it goes for now makes it a bit of a steal.
I do intend to get some clear gloss on mine at some point, i think the octopus, especially the suckers will benefit a lot.