The GT5 flares are fiberglass from the factory.
Having seen the photos I would have little doubt this is an original GT5 and one in very nice condition. The delta wing would appear to have been raised and angled over original position.
As for value; in this market a car is worth what someone is willing to pay and you'll likely get different opinions. Personally I'd hazard a guess at low value $57.5K, high value $70K and expect that you should target $65K if considering selling. That is without knowing the engine or transaxle history/mods.