You can lose 20lb *per corner* in wheels and brake discs on a car with the 21's, alone. Solid steel rotors that big are heavy as hell compared to a quality two-piece floating rotor, even a steel floating rotor with aluminum hats could be worth 7-8lb per rotor. Nice thing is, the car seems to need a rotor upgrade anyway (at least, to make it through a PPIHC run, or several drag runs in qucik succession, without fade) so you get to go faster and you get to shed heat faster too, there aren't many free lunches in car mods but that comes close
The glass roof is a dumb cost-saving feature for the factory to save production steps that could be replaced with a glue-in CF panel and some sound-deadening and drop many pounds as well. And, would be totally reversible. And you'd have shade, finally, inside the car!
CF roof panels for other platforms run around $3-5k with install. Just gotta get somebody to believe there's a market and make one. There are people doing this in the states. And that's installing onto a steel roof equipped car, drilling out rivets, etc.. With the glass just stiting there glued in, install shouldn't be too terribly expensive
8.99x - doable, if you're a crazy person, and you can get the track to prep for you juuuuust right, maybe at altitude (I imagine you only want the first 330' prepped, or less, and you want as little rolling resistance as possible after that). Rimac-beating accel? I think we'll have to wait for the Roadster for that, if it ever comes