I'd be inclined to remove the fork and give it a good cleaning and inspect that rust. I'd hate to see the fork snap and you wind up ruining that bike, and possibly injuring yourself too. Tange decals can be re-created, riders can't. Remove all the rust you can and give it a good spray with frame saver to prevent further rust from building up.
As for the frame, I'd definitely remove the after market "ugly" stickers and give it a good polish. A new straight razor blade will remove the curls at the edges of the factory decals and prevent them from tearing unless you're really good with clear adhesive and a toothpick.
Again - great find, but please be careful with the fork if it's as rusty as you say it is.