So I finally got my IRL Dominion sets back, and I did some playtesting of this card. It turns out to be a little stronger than I expected, especially for Big Money. FYI, here's the final text of the card:
Emerald Mine -- Action -- $5
Trash a Treasure card or a Victory card from your hand.
If it is a...
Treasure card, gain a Treasure card costing exactly $3 more, and a Victory card costing exactly $2 more
Victory card, gain a Treasure card costing exactly $1 more and put it into your hand
Emerald Mine/Big Money can get 4 Provinces and 2 Duchies in 15 turns (usually with 1 or 2 Estates remaining). I know Smithy and Envoy are a little faster, but they don't get the Duchies. So bottom line, this is a good Big Money card. Interestingly enough, it seems to do worse on a 5/2 start. I suspect this is because Emerald Mind would rather trash Silvers than Coppers, so it's actually better to wait until you have a few of them.
I tried it with buying two Emerald Mines, and I also tried it with a Spice Merchant/Silver opening. I figured Spice Merchant might be a good helper, since it clears out some of those Coppers for you and draws a bit. The result was about the same, though.
I also tried it with Silk Roads, and that was a lot of fun. I had all 8 Silk Roads, 3 Duchies, 1 Province, and 3 Estates by Turn 17.
Anyway, I'm wondering if these results suggest I should gimp it a little. I thought about adding this clause: "When you play this, each other player may reveal and set aside a Victory card. At the start of his turn, he discards it and gets + $1." Thoughts?