I dont know under what circumstances these cards would go up independently of each other but they clearly are and if all we did was look at spread we could probably make a few educated guesses about future price increases irrespective of EDH use
Along with Captivating Vampire, Bloodline Keeper is one of those must-have cards for any Vampire-themed deck
While it never reaches the ceiling of Toxic Deluge or Damn, it does give you a reanimate if you put seven mana into it, which makes for some nice late-game value, and makes it attractive for X-spell and big mana decks
Transforming it does have the potential to give you a lot of value, though
It puts a -mana tax on each of your opponent's instants and sorceries, and if they don't pay it, the consequences are dire
Sure, the math can be difficult to track, but when you have 20 tokens, one of your creatures gets +20/+20, another +19/+19, another +18+18, and you know the rest