It’s still early in the Z System’s history as I write this (five years), so probably early to give advice, but here are a few thoughts on the cameras that have had some sort of update so far:
- Z50 — The Z50II is the upgrade you were waiting for. Far better autofocus and Z9-level control customization are worth the upgrade.
- Z6 — The Z6II is a modest upgrade I'd say to skip. The Z6III, on the other hand, is a compelling tour de force upgrade of this original body, and even the Z5II is pretty compelling over an original Z6. You won't believe the increase in performance, the addition of so many (useful) new options, and the added customization the Z5II/Z6III will give you. The Z5II/Z6III are definitely worth a strong look if you're still using the original Z6 (or even the Z6II).
- Z7 — Good news for you Z7 users: it’s unlikely that you need the things that changed in the Z7II. (Many of the changes are the same as with the Z6II.) Most people opting for the 45mp version of the camera are doing landscape, travel, and general photography. The 900 second shutter speed might be useful, as well as un-cluttering the display are probably the most interesting changes to the Z7-type user. If that’s the case, the II advances probably don’t provide you much bang for the buck. Stick with your Z7 and wait until you see what the Z7III brings. That’s generally been my advice, anyway: skip a generation of camera before upgrading.
Should you just upgrade to a Z8 or Z9? A lot of folk already have. But you’re talking about a much more expensive mirrorless camera than you had, as both models are significantly bigger and heavier than the Z5/Z6/Z7 bodies. Sure, the feature and performance lists of the Z8 and Z9 are extensive and state-of-the-art. Moreover, with the Zf and Z6 III options, the Z5/Z6 user now has two excellent choices that aren't as costly as the Z8 and Z9.