EDIT: Ninja'd by Soulnet!
Theoretical question: how much crazier would expand be if the 3 was a 4? Just asking because King's Court effectively does twice what throne room does once, so it wouldn't be completely out of left field to have expand have twice the effect of a remodel.
Extrapolation time!
Double-Smithy; +6 cards, $7.
Double-Sea-Hag; $7; each opponent gets 2 curses.
Bah, that's a low blow. Playing a card has a cost in and of itself (one action and one card, at least). Notice that I say that king's court is twice a throne room, not 150% a throne room.
So double smithy would probably not be +6 cards. More like +5 cards. Which yeah, probably still is too strong, but +cards is the strongest bonus you can add (aside from +action to a terminal card, maybe), so extrapolating smithy is tricky. You can see though that moat costs 2, smithy costs 4, hunting grounds costs 6, if you want to extrapolate that.
Double sea hag for 7
seems alright though. It's not going to be useful for long, and by the time you get it online, the other player would have probably already developed a deck that can deal with the incoming curses.