This has been answered alot of times.
Standard bonnet is about 16.5kg, Turini c/f is 8.5kg, CFX c/f is 6.5kg Phils flat bonnet is 4.5kg (built for lightness not strength)
Standard hatch is 9kg (metal only) fibreglass was about 5kg I think.
(all weighed on my bathroom scales)
Lexan instead of glass saves abit as well, maybe about 10kg all round.
As far as stealing goes, yes I agree but the standard car isn't that hard to take in the first place (like most other cars)