Tried something similar to this. Things that would need to be fixed would be certain cards become useless, ex: detect magic, augury, evade. Its more possible to come across a very difficult barrier that cannot be passed. With the ability of people taking on what they are good on then boon coming out, it becomes too easy to acquire good cards. I agree your deck running out works well enough as pacing so a blessing deck is not needed.
To balance these things I would suggest creating a more randomized encounter format similar to how the game already is. Additionally, rather than following boon from the card perhaps it could be a roll 1d6 to determine type of boon, then 1d4-1 to determine how much.