Agreed. Also, a setup like this isn't just going to cool a GPU significantly. Doubt it'll change the GPU temps at all really.
About 10C based upon my experience. The typical SLI setup results in the top card being 10C hotter than the bottom card. In a typical case flow scenario, testing with a fog machine shows a situation similar to what is seen here (1:00 mark) except there is no air flow between the cards.
https://www.youtube.com/watch?v=dkRJsjuvQVY
I put a fan on the back of the HD cages on our SLI builds to perform this very function and it results in an immediate and effective 10C drop on the top card. As for water, ... and I say this as an avid water cooler typing from a water cooled SLI system, there is no performance reason for water cooling with the 9xx series cards. Your, as well as the card manufacturers, hands are tied both legally and design wise as to voltage modification.
And the design is so efficient that there is no thermal barrier to be erased with water cooling. You gain no advantage bringing the GPU down from 65-75C to 50C when the throttling point is 85C. And if using a CLC, our chances of diminishing the cards overclocking ability may be diminished as many do a poor job of VRM cooling which is what usually limits OC'ing on air cooled cards.
So yes, this will undoubtedly improve the cooling on air cooled, especially the top card. That is not why this thing exists however. This is a "wow" feature and it exists primarily for shows and for modders ... those doing exacting builds where aesthetics is a primary criteria. If you are picking components where the RAM, MoBo and GFX card colors are of more or equal consideration, or you are paying price premiums for other aesthetic improvements,your not gonna balk at the cost of the bridge.