On this one I totally agree with you. There is VERY little stress on the mag (ti?, I think mag) panel covering the roof frame. There is absolutely NO REASON not to offer an optional fixed polycarbinate panel for the Z06. I think they would sell well and represent a good compromise for those who want the Z06 just a bit more than they want the targa capability.
I was one of those proposing this back before and shortly after the release of the Z06. We know GM watches DC, so it's good you brought this up again.:thumbsup: