Interesting!
Coppersmith's not my favorite. In this game, it usually provides you about the same benefit as a silver, is worse than a silver once, and is an amazing gold equivalent on turn 5.
Contrast the envoy. If you buy no other action cards but an envoy, he's essentially always as good as a silver and is very often much better. Also, you're very happy to draw Nobles Envoy x x x and very sad to draw Nobles Coppersmith x x x (which happens to you in the late game).
Now, there are boards where coppersmith is amazing, but they tend to involve lots of swingy high-power cards (wharf or king's court come to mind, although the less powerful, but still quite powerful, apothecary comboes well with coppersmith). But generally it's one to look past.
By the way, on this board, I'm very tempted by highway and trade route to try to build a crazy mega-engine. But although I would probably play it this way, as it would be more fun to play than a basic envoy strategy, my suspicion is that the basic envoy strategy wins out.
edit: crossed jonts, with whom I agree.