My insurance rates when down when I bought my Tesla. Of course I don't have a performance model.
The Performance model was more expensive than a regular S, but even the regular S quotes were more per year than our newer Audi S4 (My first CPO order was a S85 before I switched to the P). If I had bought a new P85, I might expect that, but mine was used with 40k miles. Should be equivalent in value to the S4 at this point. I would guess my Model S is safer than the S4, which is why I attribute the raised rates to high repair costs. The S4 is an aluminum car as well, so that isn't a factor.