Arne,
I have attached a picture that I had to hand (full frame & a 100% crop), but I'm not sure that you can learn much about the Makina W67 from it as:
1. It is scanned on a Epson flat bed scanner. You would need at least a high quality medium format film scanner (Nikon 9000ED or Minolta Multi Pro.) or preferably a drum scan to show what the camera/lens is cabable of. (Unfortunately I can't afford one).
2. To get a resonable file size to post these are "8" quality jpegs, which obviously degrade the image.
3. Original is Fuji HR400 Colour Negative.
The 55mm Nikkor is a very good lens and at least you can see from the attached that the "drawing" is good.
I love this camera which I purchased secondhand some years ago for about 600 GBP ($1,000) , but would I buy one secondhand now? I think only if I really loved the way it handles (which I do) and needed the compactness. Secondhand prices in the U.K. high, now about 1,000 GBP ($1,800) and the cameras are a lot older now, so are more likely to give problems.
I have only had one problem with my (now rather worn) W67 example a few years back and that was the shutter linkage breaking. Fairly common (happened a few times with the 80mm Makina 67, I had, where the linkage is longer because of the greater bellows extension.) but it was not too expensive to repair at the time in the U.K. My understanding though was that Fotoadvise, the then U.K. importer had brought all the remaining spares from Plaubel when they stopped production. I'm not sure they are still around or what the spares situation in the U.S is. So be aware as others have said that spares may be a problem.
Other problems are the rangefinder getting out of alignment (commonly caused by folding the camera closed without returning the focus to infinity, a real no, no especailly with the 80mm version), the light trapping in the back disintergrating (its made from plastic that goes sticky), both these happened with my 67 80mm. I have also seen the meter not working (usually poor contacts or corrosion in the battery compartment) and one would want to check the bellows carefully for pinholes, although I have never had any problem with the bellows on my two examples. I would not buy without seeing and checking carefully for all this and preferably running a film through before purchase. I think most of these problems are unlikely to need parts replacement and any competant repairer should be able to deal with them. (and there are companies that supply replacement bellows).
The Mamiya lenses are as good as the Nikkors (I have the 3 lenses for the 6) although I think I personally would prefer my 55mm over the 50mm on 6 x 7, and you do have to use a seperate viewfinder on the Mamiya - a disadvantage I think. You do have the choice of the 65mm lens of course. The Mamiya 7II is still in production (I think, but things alter quickly in the film camera world these days) and in the U.K. good secondhand 7II bodies go for 550GBP (400 GBP for a 7) and a 50mm lens and viewfinder is about 750GBP (all dealer prices). A S/H 7II and 65mm (no viewfider needed) would be about the same price as a S/H Plaubel, at least in the U.K. and with the 50mm only slightly more. I think it would be the more reliable buy these days unless you can't live without the particular qulities of the Plaubel.
Jim