The 2000-02 actually had a polycarbonate (
http://en.wikipedia.org/wiki/Polycarbonate) sunroof which is FAR lighter than glass. but tends to scratch easily
2000-02 was drive by cable, 03+ went to drive by wire.
03+ was now available in yellow and had HID headlights as an option and new front and tail lights
GTS - 00 & early model 01's have the ecu which engage lift at 6000 rpms, all other years engage at 6200 rpms. 00, 01, 03, & 04 have fuel cut set at 8350 rpms. 02 & 05 are set at 7800 rpms. Lift bolts were reinforced in 03 along with the interior and front facia lift.
so gts-00 is has more performance
as for gt issues the 2000-2002 had oil consumption problems but in 03 the oil passages were fixed and no longer consumed oil.