I will also come to the defense of Expand over Forge.
Forge is certainly more useful in the early game. I would rather have a Forge on Turn 3 than an Expand on Turn 3. But unless I've got Baron (or Mining Village, I guess? I'm sure there are others) to work with, odds are I'm not getting either card on Turn 3.
The later the game goes before you can actually get these cards, the more useful Expand seems (of the two). You want Forge to do heavy-duty trashing, but the mere fact that you want Forge probably means cheaper trashers weren't available. So by the time you actually get Forge, you've sort of missed the valuable trashing stage of the game. Not every time, of course, but Forge becomes pretty dependent on what it gets drawn with in a big deck.
Expand is also sort of random in what it gets drawn with (by the time you can afford it), but decidedly less so than Forge. You only need to draw Expand with one other good Expand target, whereas Forge needs at least two to be worth it in most cases. Also, I can see picking up Expand in a deck that already has good trashing as a means of snagging an extra Province or Duchy somewhere. Less so for Forge.
Ultimately, I would say that the $7 cost harms Forge much more than Expand, since Forge is a card for the early game, and Expand is a card for the mid-late game.