I figured I would revisit this to correct some of the worse comments I made.
In general, "Gain X Horses" can be treated as "+X cards" for power level.
Horses are better than +X cards. The benefit of saving extra Horses makes up for the 1 shuffle delay in getting your draw.
Stockpile is insane, especially in 2 player. I'm still not sure how to play it, all I know is that if you play against someone who skips it you tend to win. My suspicion is that early on, you want to get all your Stockpiles off the mat before your reshuffle, but after you get a few, you only want some in the reshuffle.
Stockpile is still insane. I also still have no idea idea how to play it, but your goal is much closer to trying to get all your Stockpiles into the shuffle.
Cavalry's top portion is kinda eh. Its bottom portion is insane. Quite nice with trash-for-benefit.
Still true but I don't think I conveyed how good the on-buy effect is. It's
really good. $4 and 0 net buys is a low price for getting to try to save your turn by drawing a card you need, or shuffling in cards you just bought. And the top half of 2 Horses isn't as bad as I thought it was. In Cavalry games, you tend to be overterminaled because you buy Cavs to rescue your turn, but another way to put it is that you will always use up your available actions and those actions will, at worst, turn into 2 Horses each when you play your leftover Cavs.
Groom is great with Alt-VP rushes, and even outside Alt-VP rushes, Horse gains on your actions is good, and double Silver gains for money decks isn't bad either. In engine games it's already worth opening Workshop to gain $4 cost actions, Groom is the same thing except you get Horses along the way.
Understates how good Groom + alt-VP is. It's not just good, it's centralizing. It's almost disgusting how fast mass Grooms can empty the Estate pile, or itself. Given 1 Groom + 1 Horse in hand, and an empty draw + discard pile, you can do Groom -> gain Groom + Horse -> play Horse, which loops, converting 1 action into 1 Groom gain. It's a very easy setup that makes it possible to end games out of nowhere.
Barge should usually be played for your current turn, but if it's your last action and you have a decent buy in your current hand, playing for next turn is nice.
I think that if Barge is your last action, you should default to playing it as duration and be looking for reasons why you want to play it this turn instead (normally the answer is that you really want the +Buy).
Similarly, Wayfarer is insane - it's arguably the strongest in the set. (Or at least, if you argue it is, you won't be laughed out of the room.)
Hahahahaha no if you argue Wayfarer is the strongest card in Menagerie, you'll be laughed out of the room. I blame playing too many Wayfarer-Counterfeit games at the time of writing. In terms of power, Cavalry, Stockpile, Groom is a clear top 3, and then Wayfarer vs Scrap are competing for 4th and 5th.