First impressions of the cards themselves:
Royal Blacksmith looks like it will be really strong in any deck that has a way to trash Treasures (Mine might actually be worth it here, if there's nothing else). It is expensive, but the debt makes it a bit easier to buy, and the strength looks better than Hunting Grounds. Another thing to note is that if you play two, you've already discarded some Coppers, so the downside isn't as bad the second time.
City Quarter looks good, but it will need the right deck. If you are playing this without at least 2 other action cards in hand, you probably bought it too early. It works extremely well with start-of-turn draw effects (Wharf, Caravan, Haunted Woods, Prince, Dungeon). Other non-terminal draw cards can help out as well if your deck is at least 50% actions. If you can draw enough actions in your starting hand, this card can stack explosively, similar to Madman or Crossroads.
Capital seems risky. Here's a thought experiment. Let's say you buy this over Gold. (I know I'm comparing it to a $6 card, but Gold is a good comparison point for a lot of $5 cards.) Compared to Gold, on the turn you play it, this card gives you +$3, +1 Buy now and -$6 next turn. Is that really worth it? My guess is that most of the time the answer will be no.
Obviously there are a lot of weak points with my thought experiment. Capital is better than this scenario if you don't have another source of +Buy, if you only have $5 the turn you buy it, if you play it on your last turn, if you need to spike large amounts of money quickly for King's Court or something similar, or if you have a way to keep it from being discarded (Mandarin, Counterfeit, Herbalist). Overall, I think it will be a situational card, and I don't see myself buying it very often.