As a recent 67 owner:
It's heavy and bulky, my heaviest camera combinations have been around 1.5kg thus far. My 67 + metered prism + 105mm weighs in at 2.3kg+, and it feels heavy on an OpTech strap.
Worth is very difficult to pin down, due to the myriad of potential accessories it comes with. I went for a newer 67 over the 6x7, but not the 67 mkII.
The mirror slap is loud, but like the Hasselblad mirror slap I think it's a touch overstated. If anything, it's the sound of the air that the mirror moves that makes a distinctive noise.
I was very happy with the first roll that I shot with it - beautiful images.