I probably wouldn't hesitate long before buying a 33MP ZD33 for 20.000 US$, or a universal back with the same resolution for 16.000 US$.
I'm shopping around too for a Mamiya solution. I've looked at all the available and soon to be MF cameras -Rolli, Hassycon, Mammy - and the "old" Mamiya with a clip on back appeals to me most, the finder seems much better than that of the ZD, and you can get easily at the CCD for cleaning. Also, I hear the imagery is better with the backs but I cannot verify that.
Bernard, have you tried the two side by side ? I really think the old Mamiya is as fast to point and shoot as an SLR. I tried one for five minutes with a Phase back, and was quite happy immediately with finding my way around it and with the resulting images. The one thing Id be worried about is mirror slap. And if a body dies you just get another one off eBay. Everyone agrees that digital backs have extremely few hardware issues while bodies have the same bunch of problems as any moving-parts machine.
I also tried a Hasselblad, but there I really don't like the finder, and the resultig images looked strange. Like every thing else that is being displayed from that camera in fact. It's that weird software processing they use and their back - I've seen imagery which was taken with Phase on Hassleblad that looked good.
There is a new trend, very strong at Photokina, to have imagery manipulated completely by the software - at the Phase booth when I said I wanted to see an image without any modifications at the Raw level they looked at me really strangely. Leaf, Phase and Haselblad are pushing their software very strongly, and pasting complex profiles over every image, and Haselblad are doing a lot of in-camera lens aberration correction which also affects the "look" of the files.
It's becoming harder and harder to separate the camera "look" from the look of the camera software.