I am in between....
I believe that if you can improve the car mechanically with better suspension, engines, transmissions, brakes....modifications that improve performance, comfort or safely...I am all for such modifications from the original. This would include better seats than the originals.
However...when it comes to the overall appearance of the exterior...I would prefer staying as close to the original as possible with a few deviations. I.E. Omitting the rivets and two piece design on the hood scoop and the perky butt....for example... are not deal killers. I might even consider a change in engine compartment vents as being acceptable if it improves cooling performance.... without getting too obvious or gaudy.
If the modification is in the interior, engine compartment or trunk and not immediately visible to the outside...yet provide an improvement to the function of the car...such as a dropped trunk...those mods are fine.
But for the recessed rear plate...I would pass. It just looks too "modern" and out of place on a 66-66 era Cobra.