Well I guess you are getting a lot of the same answers. Pentax 645n is one of my absolute favorites! It is significantly improved over the 645 original. But personally I don't think the minor improvements of the 645nII warrant the significantly higher price. As for the lenses, the are fantastic! I only use the manual focus A series but love them. The 645n even has focus confirmation if you are unsure about your MF abilities. It can also imprint the exposure data on the edges of the film for each frame. The VF is large and much brighter than the 645 original and the ergonomics are excellent. It is a reasonably portable camera with a very sturdy build.
The 67 is much larger, not nearly as easy to handhold, but is a wonderful camera in its own regard!
As others have suggested, the Pentax Forum is an excellent source for information.