The only person that would find that motor more valuable than any other 302 would be the owner of the Shelby that it came out of. Other than that, it isn't a valuable motor. If you have the original carb for it, that would be worth about a grand, but, that would be the only valuable component.
As far as getting more out of it goes, some nice, free-breathing headers would help, and, not running the single, transverse muffler that the car would have had originally. Something like a 3.50 rear end would wake it up some. It's really all a question of how much money you want to throw at a build.