The first reply to the OP severely understates the value of the cards in the C-deck. Here are the significant ones:
Deathbane Light Crossbow +1 - Fan favorite, d8+1, +d8 if monster is undead
Glaive - d10, discard to reroll if you fail
Greatsword - 2d6 (!!!), discard to add strength die
Icy Longspear +1 - d8 + 1, doesn't need proficiency
None of these weapons will last through AD6, but they will stay in your characters' decks for a good long while.
Augury - An addiitonal copy of this powerful spell is massively significant if your party has enough spell slots to hold onto it
Inflict - An additional copy of this spell is important if you're going to play with Lini
Crown of Charisma - Auto-succeeding at diplomacy checks is very strong. Diplomacy picks up a lot of allies, closes quite a few locations, and even comes up sometimes on villains/henchmen. Also significant is that this card doesn't exist in the base set. It will stay in your party through the end of AD6 and its absence is keenly felt.
Amulet of Mighty Fists -- Adds 1d4 and the magic trait if you don't use a weapon or an attack spell on a combat check. As a basic, it's a nice starting card for Sajan, Lini, and Merisiel.
Masterwork Tools, Spyglass -- These are practically the only really good items in the entire base set, so an extra copy of each is welcome. Will likely stay with your party all the way through the adventure.
So let's get back to the original question at the crux of the OP: "Is there anything really amazing in there?" Yes. The good new boons, as well as the extra copies of existing powerhouse boons, are totally worth 2,000 gold eventually. Whether they're worth it to you in the short run, at the expense of unlocking more new characters faster, is a tough subjective call you'll have to make.
Also, though OP didn't ask about this, Doppelschwert is right in pointing out that the C-deck is "kind of a mixed thing." It adds the following monsters, which are all really annoying in different ways:
Plague Zombie x 2
The Enchanter and Siren are particularly bitchy, and I'd be lying if I said that I don't sometimes feel as though I'd happily give up all the Auguries and Deathbane Light Crossbows in the world to never see a #$&%ing Satyr again. Seriously, #$&% Satyrs.
Of the 6 barrier cards added, 4 are "friendly," 1 is very challenging (Explosive Runes), and 1 is at minimum a hideous annoyance every time it appears (Skeletal Horde), so while they're not as bad as the monsters, the C-deck barriers also add some annoyance to the game.
So if you're on the fence about the C-deck, trying to decide whether it's "worth" it, you need to consider that the cost of its boons isn't just 2,000 gold -- it's also the pain of putting obnoxious banes into your game box that (in the digital version, anyway) you'll never be able to remove again.