I seem to be in the minority, but I really haven't had a problem with heat through the glass roof, and I pretty much never notice the sun overhead. Yes, it will get hot to the touch, but if you're not needing to be in hypermiling mode and can crank up the AC (like any car when starting out initially), it will cool down nicely. As
@Adnillien said, the recirculation also helps.
As for windshield chips, I guess I'd need to know the difference in cost in replacing the GT one or a non-glass roof one, so that could definitely be a factor. I will say that I won't invest in windshield tinting simply because I don't want to add that replacement expense. Maybe if I can go a year without a chip, I might reconsider.