So I've been running some rather crude simulations with Chris' DominionSim (I'm still having trouble figuring out how to tell the computer to buy cards the way I do), and if we just substitute in Soothsayer for Witch in his DoubleWitch code, and play DoubleSS against DoubleWitch, Witch comes out a little bit better. What's interesting is that adding a 3rd Soothsayer pushes it a percentage point in DoubleSS's favor, which is weird, because DoubleSS seems to do better against BigMoney than TripleSS (though both trounce BM quite nicely). Now, if you run all three together (DoubleWitch, DoubleSS, BigMoney), quite obviously Big Money loses, but Soothsayer seems to mostly come in only a few points ahead of it: BM takes 10 Curses on average, DSS takes 6, and DW takes 4.
My personal (possibly wrong) guess is that this is because Witch just sees SS as another Witch that draws it another card, and makes good use of that, especially since Witch draws extra cards anyway, almost turning Witch into a Smithy, and SS's Gold-gain doesn't seem to be enough to overcome this. The card draw (which only Witch is getting here) means that Witch cycles more, which means Witch gets played more.
Here's where it gets more interesting: add in a bot that buys one Witch, then one Soothsayer (preferring to play Witch). In the 3-player game, DW still narrowly wins. But if we drop the BM player, WSS now narrowly wins. In both cases, WSS takes fewer Curses and gains more Golds; what exactly is it about having that third player that gives DoubleWitch the edge?
Now things get weirder. If we throw DoubleWitch, DoubleSoothsayer and Witch/Soothsayer all in the same game, now DSS is the favorite. But it's not by much:
SS/Witch 32.5% (3254)
Double Witch 30.4% (3036)
Double SS 37.1% (3710)
DSS ends up taking more Curses, but also more Provinces!
I think the lesson here is that adding a third player just fucks up everything and I should probably go do grown-up people things now.
Oh, right, a reason for posting this *not* in the Simulations forum: anyone with real-game experience with Soothsayer have any thoughts on this?