Your comment about "conjured" is a nice catch, I think, it fits with my impression that Sheridan is subtly invoking the spirit of Shakespeare's Tempest--Prospero does indeed conjure up the tempest that brings the ship to the island.

I also wonder whether gout is the only thing that brings Sir Anthony to Bath so abruptly. Look at what he does the minute he gets there--he wastes no time in getting to Mrs. Malaprop, and in short order he makes her a proposition that they join forces to bring his son and Lydia together. Is it possible that this is the primary motivation for his coming to Bath?

He may be scheming as much as these other scheming characters, but we may just not be privy to all of his motivations.