1. Its a spider 2/3 the size of a skyline. They dont remove weight from the car at the expense of safety, that is against all design rules and engineering principles. The only difference is there is much more of a crumple zone in the front end which will absorb frontal impact more effectively ie not shoving an engine through the firewall at your legs.
2. Look back and see when airbags came in, check the saftey requirements of seat belts between 1993 and 2003. Increased technology determine the positions for crumple zones for better shock absorbtion.
Your friend in the suburu had an accident and hit his head, why is he more likely to hit his head in a smaller car?
No seat mounts will not help in a front collision as there is no force against the seat.
No it does not sound cool that your mate hit his head though it had nothing to do with the weight of the car.
There will be more overall inertia in a heavier car, not because of the the position of the engine. With a mid engined car there is alot more room in the front for shock absorbtion.
3.Stock for stock the mr-s is more a performance vehicle than the gtst. Lets start with the mid mounted engine for a better centre of gravity, shorter wheel base, very decent sized brakes for the 1000kg vehicle it is. It doesnt have a roof because it was not designed to have one, not to save weight.
If you think you are protected in your skyline cos it has a roof then you have obviously never seen a car land on its roof. A roll cage will benefit any vehicle that suffers an impact to its roof. Lets face it 300kw in a gtst is not as stable as it is in a gtr(the real performance variant of the skyline). With its weight you would not need 300kw to make it a weapon that would be overkill and beyond the vehicle standard limits just like in a standard chassied skyline which is also not suitable for 300kw.
4. Yes the s2000 is a performance vehicle, why is it safer to be in an s2000 than an mr-s in a collision. You state that the s2000 has a more sport oriented chassis which i already know though how does this help when you are already out control?
As for light cars being less safe and or rigid check out Smart car crash tests done by topgear, it should be on you tube.