Personally, I don't care much about the Android version updates. The Xperia Z works extremely well under 4.3 and there's actually no real need to update to 4.4.2, in my view. I have the Xperia Z1 as well, and recently updated to 4.4.2 but it actually worked well under 4.3 and I don't really see that significant an improvement after the update to KitKat. I would be more concerned with the updates that fix bugs (but still under same Android version) as these would improve overall performance and squash issues.
Notwithstanding the above, Sony do tend to roll out the latest Android version to the latest devices first (e.g. Xperia Z1 before Xperia Z). But they do commit themselves to doing so for devices that are less than 2 years old. For example, KitKat is planned to rollout to Xperia Z this month