Buying all 8 Castles (2 player game) is worth 41 points, NOT counting the Duchy and the 1 vp for on-gain bonuses, or the variable vp for the other on-gain bonus. So just 1 point shy of all 8 Provinces, and way less total cost ($52 instead of $64, plus you only need to hit $8+ 3 times).
Yes, but you're taking the risk that you won't get all of the Castles. If your opponent snipes just the King's Castle, then you've paid $42 for 24 VP (plus bonuses) in seven cards, which is not nearly as compelling.
Castles really shine in 3P, though; there are a lot more points up for grabs.
Yeah, just like Dukes, the the pile as a whole is worth a lot less if you split the Castles (or the Duchies) evenly.
Also, I suppose you (Gendo) counted the points with untrashed Crumbling and Small Castles?
All in all, I doubt these will be an alternative main source of vp like Dukes, Fairgrounds, Vineyards and family can be.
I think they'll be more like a tactical battle ground, where you can try and gain an edge over your opponents. While the potential for scoring big points is there, your opponent really needs to be kind to let you get away with the full pot.
I like how these will "give out roles" to the players: one will have the Humble Castle, the others will be the contenders.
The art, it is beautiful.