The IID is much, much more expensive than either the II or the original rz67 solely because of the digital back compatibility. If you don't need digital compatibility, get an earlier model. The original is about $200-$250 used and has 95% of the IID's functionality though it might be harder to find one in very good condition.
I have an original rz67 and it's fine, but it's not light. I don't think it's much lighter than a 4X5, which, to be honest, I might rather have... The lenses are very heavy, too, and heavier than large format lenses of equivalent focal lengths.
I use mine mostly for landscapes so far, but the Pentax 67 and Mamiya 7 both have wider lenses and might be better landscape cameras. I chose the rz67 over the rb67 because of the 50mm uld (which is reasonably sharp and generally just nice) and the 110mm f2.8, which is remarkably sharp, even wide open.