I have thought about this nonstop for months... And still spend most my free time thinking about this exact subject. I've shot many many rolls of 6x7 and 6x9, and this summer I started getting into large format. It's tough, because I don't even print at this time, so some people on this forum would laugh at the idea of shooting larger formats without a need for large printing, but it depends how you approach the medium.
Just about everything I want to shoot can be handled by the rz67, but trying other cameras is a lot of fun, and whether or not the quality is much greater, the qualities (or charictairticstics) are much different, and therefor give your work range or give you a new challenge. I love the excitement of learning something new. Right now, just three boxes of film into it, I find every image I shoot on large format a challenge, a thrill, and a delight. I'd say if you have the means, give it a shot. For what it's worth, my landscapes are looking pretty surreal on large format, even just scans. Not only does it force me to be more selective and meticulous about my compositions and subjects. That gives you a better end result.