Well, bonnet don't matter cus' it's a bolt on item. Same as front wings, bumpers etc.. easily swapped.
The bits I'd be dubious about painting are rear arches, roof and sills - cus' once they painted, thats it. If rust gets bad on the rear arches, I'd probably paint them.. but I'd probably wait months looking at different jobs to get the best done.. dunno, wanna enjoy it being none-painted for now
Stonechips etc.. paint the bonnet, cus', if I ever wanted an unpainted bonnet, I could wait for ages and when one comes up, just put it on.. heh.
Guess it again depends on what ya want from a car..