Even if your [3] doesn’t apply, I believe the Casimir effect doesn’t scale fast enough — even a cavity made from proton-sized parts will never exclude more vacuum energy than the mass energy of those protons: https://kitsunesoftware.wordpress.com/2017/04/20/can-a-casim...
There are more realistic explanations[3] for the Casimir effect however, so no Alcubierre drive for us anytime soon.
[1]: Think it was this show https://en.wikipedia.org/wiki/Sci_Fi_Science:_Physics_of_the...
[2]: To be fair, Alcubierre suggested it himself first
[3]: https://en.wikipedia.org/wiki/Casimir_effect#Relativistic_va...