Boneyard has different weaknesses than Vulture, and for the most part they're more common. PC, mass-CC and small shields all make the offence of Boneyard completely useless. Additionally, some games it will fill up your field and you won't be able to play higher-impact cards. Graveyard is an enormous improvement and the mass-CC weakness can help feed your BW with either card, so it's an alright replacement for Vulture, but its advantages rarely come into play.
Cat decks can be customized a fair bit. I enjoy a version with Purple Nymphs and Arsenics, for instance. Cal's particular build is good for stallbreaking, but struggles with shields and though it's pretty fast, it could be even faster.