I have test ridden the Vectrix when it first came out in the U.S. and of course I own a 2012 Zero S, too. I think your observations are correct. The Vectrix was very stable, especially for a scooter platform, but it was definitely not "flickable". The Zero is kind of "squirrelly" at high speed when going around bumpy corners, but it is great around town, where its quick handling is a positive trait. I hear that the 2013 models have a larger chassis and should handle better. However, the Zero is much faster than the Vectrix that I rode, which topped out at 60 mph. Plus, the Vectrix's range really dropped when taken on the freeway. The early model that I rode was good for about only 30 miles under normal riding conditions. I would say it had similar performance and range as the "classic" Enertia.
I am really looking forward to reading an instrumented test and objective comparison of the Zero S and the base Empulse models.