It depends. The 302 outwardly is the same size as the 260 and if the swap kept a period intake and carb, generator mount and so on there's be very little obvious when sitting to tell them apart.
Most guys however "jazz" them up with non period accessories and chrome work and along with it tend to modify other parts of the car from stock condition. Depending on what's been done and how well, it can even enhance the price. I know guys who have gone as far as stroking their 302 to a 347 with dual carbs and in one case nitrous.
Personally I still run the stock 260, although 260 specific bits like pistons are getting hard to get. But I like it in stock condition rather than a fire breathing monster.
Worth is in the eye of the beholder.