It depends. If the current cable is really defective, you'd get a long-term benefit from renewing it. If the old one simply has normal wear, you might not notice much a difference in the two. You might want to see if you can sample a few other GTs of similar vintage to see if their clutches compare to yours in terms of pedal force. That might help you determine if yours is defective in some way. Or perhaps the previous owner of the car installed an upgraded clutch that has a higher pedal force than stock...
Keep in mind that the GT's clutch is going to be stiffer than, say, a V6 Camaro. Even in stock form, the engine has 300ft-lbs of torque and is driving a fairly heavy car so the clutch has to be fairly ballsy. Did you drive the car before buying it to determine if you'd be able to live with the clutch effort and your disability?
It may be possible to find a multi-plate clutch to replace the single plate one that's in there. Many are oriented toward 1000+ HP engines but perhaps you can find one intended to replace OE parts. MP clutches can theoretically have reduced pedal effort because they don't require as much clamping force (i.e. spring pressure) to handle the same torque. Spec's "Super Twin" might be one example. (Note: Just throwing ideas out here...I don't know if Spec's pedal effort is lower or the same as OE: check with Spec to see if they might have something you can work with...)