Some states (California for instance) make it more practical to own an older 1971-1974 Pantera revised with a kit, rather than owning an actual GT5 manufactured from 1979-1984. The older cars don't require periodic tailpipe emissions testing, whereas the newer cars do. In a state like that the value of a GT5 replica should do well so long as the installation of the kit exhibits good craftsmanship and the installer refrained from "personalization" and remained true to the car being replicated.
If the GT5 kit is just one part of a car that has been extensively "personalized" then placing a value on a car like that is partially dependent on the quality of craftsmanship that went into the car, and partially dependent upon how closely the "personalization" matches the buyer's "personal" tastes. The "personal taste factor" means the value of a car like that will be worth more to one person and less to another.