Sent the ruler and brick wall tests to Bjorn today! Bjorn doesn't see any problems with these tests, so I guess its safe to assume that I've got a good sample.
Anyway, in my humble newbie opinion, the CZ SAL1680Z is a great all around lens with incredible sharpness rivaling that of my prime 50mm 1.4 under the right conditions.
It completely trumps the standard 18-70 kit lens in my opinion as far as IQ is concerned. The fact that it can zoom longer, wider and brighter is reason enough for me to justify the upgrade.
I really don't have that much issue with the build quality since I've upgraded from the standard lens. I HAVE seen quality Nikon primes that my friend brought with him, but then, he uses a semi-pro/upper enthusiast D300, so the difference in quality doesn't bother me much (I'm using an entry-level A300 after all).
The SAL1680Z is expensive, but as far as I'm concerned, I'm getting what I paid for. Even my Nikon-loyal friend was impressed by it, not least of all by the Zeiss badge it carries.
Now that I have some quality tools, I think I'll continue my journey towards our common goal of being a quality photographer.
Many thanks to Bjorn for helping me test these lens!