The only time you would ever play Army of Misfits as an activated conspirator is if you 1) had Grand Market and HoP in hand and 2) also had King's Court, Throne Room, and Royal Carriage in hand, as yet unplayed. Otherwise, you would simply play Army of Misfits as King's Court on Grand Market for the same benefit to your HoP as the conspirator would have given you, plus more coins, buys, and actions.
Your edge-case requires 1) a hand of at least 5 cards, plus Royal Carriage 2) a specific set of 5 cards in the kingdom and 3) a deck where simply KC'ing your Grand Markets will be less effective than boosting your HoP. But given this unlikely scenario, I'll concede that your edge case is at least theoretically valid.