While I own a 73, I do prefer the earlier tail lights to the post-73 lights. I also think the sharkstooth grille is the best looking Duster grille. But, if it's not a sharkstooth grille, it looks kind of boring.
With that said, go for it. There really isn't that much difference and you can certainly make a post-73 Duster look as good as any 70-72.
Not my cars, but great examples of good looking 73 and after cars: