Yes, god know how much time you need to spend in the krypt to build up that many keys. And the most reliable way of getting keys is from the hanging bodies, which just keep re-spawning over time (but it's still really slow and unreliable, you mostly get hearts from them), so no need to waste coins on refilling the krypt. The reward for the 200 key tower however is the purple Jacqui skin of her in her leather 'Briggs' jacket and armoured pants. However I randomly unlocked that when I played through Aftermath's story mode I believe, so there's no point grinding for the tower if you've already unlocked the skin.