I see potential for IGG to conflict with the Coppersmith. Sure, you'll plump up your deck with Coppers, but each IGG (and each Curse) increases the chance that Coppersmith will be a dead card.
I see what you mean that two piles will run out pretty quickly. So, focusing on winning the Duchy race is a good tactic. I'm not sure that Coppersmith will do it.
When you draw Coppersmith, you'll have some possible scenarios:
* You have 0 Copper in hand, in which case this is a dead card.
* You have 1 Copper in hand, in which case, Coppersmith nets you +$1.
* You have 2 Coppers in hand, in which case, Coppersmith nets you +$2.
* You have 3+ Coppers in hand, in which case, Coppersmith nets you at least +$3.
In all those cases, you could have easily replaced Coppersmith with a Silver. In fact, for the first two bullets, you are actually better off having a Silver. For the third bullet, you accomplished exactly the same thing. For the fourth bullet, you would not be hurting if you had a Silver, because then you'd have $5 instead of $6, which is enough for a Duchy.
In theory, the Coppersmith might help you get up to a Province, but with IGGs and Curses flooding your deck, that's not very likely.