There's almost always some reason to go after the black market, access to 25 more cards, some of them will be useful, unless either you've set up a set intentionally where every card is really strong, works together and there's cursing, trashing, actions, draws, buys and no deck dependent green cards as well as no tactician, library or watchtower, or there's no +2 action cards and there are probably vital terminals like witch/mountebank/chapel/wharf and also few/poor +2 action cards from the bm deck.