I wonder do you actually lose any weight after fixing all of the rust spots, that green one could've also been better in the end if the "leftover" rust was all that you photo'd here, would've been less work left there, my guess is you decided it's unrepairable which sounds legit.
Though for a lightweight N15, wouldn't it be smarter to turbo an 1.4 Sedan? that'd be lighter than a N/A SR20 Hatchback if i'm not wrong, don't judge me though if i'm wrong there, i'm more focused on N16s and that turquoise beauty you see on the left is nowadays heavier than stock, probably should put up some pics of what i've been doing during past year.
Though who am i to talk about lightweight, i drive that thing's younger brother which weights at least 270 kilos more and has 30 horses less, stock weight is around 1360s if i don't remember wrong.