I'm not a gnx guy but personally on a real gnx I would think that is part of the story of the car. I would probably keep it if it's a low mileage type car. If its a driven car, high mileage, I personally would take it off. But that's just my opinion and since I dont own an X its not even worth $0.02
Dealers name is on my invoice / sticker....not my car. Would have removed that the day I bought it, and frankly, let the dealership know my disappointment for putting it on in the first place. Takes away from that gorgeous GNX badge IMO. With that said...car is diamonds nonetheless.
I would say it comes down to if your a purist or not, and how changed the car really is from stock. If you tell me you have done motor mods and changed a bunch of stuff from stock on the car.....then does the sticker really matter at that point.
But if the car is a bone stocker and you intend it to stay that way then hell yea I would let it ride!!! IMO
I am certainly partial to them; I remember ones in the 70's being riveted on! But in this case I think it adds to the originality, and it is pretty good proof of an original paint job with just one glance.
I'd remove it, if the car was reasonably new. Being it's 28 years old, the paint under the sticker would be somewhat "new", and would more than likely be blacker than the rest of the trunk, and you may see the shadow of the sticker.