i dont think rigidity play's in to this very well, as all the roof is, is a piece of convex sheet metal tack welded to the body and has little play in the actual stiffness of an 240z, because well there's not much strength to the roof of a 240z period, an i for the few of us who have been in a side impact in a s30, i think you would agree with my, that the roof just accordions.
(also i dont give a flyin' #@$% about resale value, i bought it to drive it and drive it i shall, whether its into a fence, wall or the ground or another car.)