I've seen some great pictures of car rad' cooled setups and certainly, if you cant get a pump with enough balls to push the fluid through (and keep the joints water-tight), they make good sense - providing you can also keep the noise down. I know that feeling about the water blocks all to well; whilst the rest of the cooling setup will be able to handle the next, and probably the next generation of GPUs, I can't help feeling that the water-block are the weak (and expensive link).
I think there is a solution though - its just not commercially available atm. I used to work as a miller, and I know I could easily have got a better finish (read smoother) than the contact surfaces of the water-blocks from Aqua Tuning that I use (I've seen the video of their production, and I'm not impressed). I cannot see why 'shims' can't be used. If you had shims that were manufactured to a stated thickness, to a very high tolerance (say 1 micron - which is quite easy to do today) with a very smooth surface finish, you could quite easily build a 'universal' water-block that contacted the shims, placed on critical surfaces) via thermal paste. Since the critical dimension is the thickness (the other dimensions are nowhere near as critical), these would be quite cheap to produce. Yes you would loose a degree of thermal conductivity, but that could be allowed for. This way, you would only have to swap out the shims for the relevant thickness when you upgraded.
Perhaps I shoud patent the idea........