I find the disorder fascinating and always try to make sense of their grand plan whenever I encounter one. Apart from self-destructive voices and religious imagery, nothing any of them have said would have been valid beyond 1900 or so.
In an era before CIA monitoring, chemtrails, fluoridated water supplies, and tailing cars, what did (supposed) schizophrenics mull over? Were they convinced that kings followed them in carriages? Was the East India Company in bed with the Chinese? Did cultural phenomenon like Napoleonic-era obsession with egyptology influence half a century of people sure that they were Bastet?
There's a fairly large difference between "conspiracy" in the modern period and before, which might be difficult to catch from a modern vantage point. Certainly, pre-modern people suffered from recognizable paranoia: murderers, spies, stalkers, thieves, and all sorts of miscreants abound in troubled minds.
However, pre-modern delusions could easily focus on the supernatural in a fashion which would be considered completely "insane" today. Historians diagnose Joan of Arc, for instance, with all varieties of mental illness to explain her connection with the Christian God. That the sole deity took a specific interest in the fate of one of the many feudal entities of Europe over another is, from certain perspectives, as much of a stretch as "tin foiling" or what have you; the CIA and God alike can both be mysterious, vast powers interfering in the course of human events.
Another "delusion": Frederick V, Elector Palatine, apparently believed that the apocalypse was nigh, and that his holy destiny was to take the crown of Bohemia and begin a cataclysmic struggle against the Papist forces of the Catholic Emperor.
Because materialism and empiricism have restricted the forces and powers within our world greatly, paranoid delusions in our time rely on illogical abuses of power by worldly groups, on often absurd scales. For the pre-modern mind, however, spirits, demons, devils, and deities actually had the power to watch you at all times, to curse you, to crown you, to control kings, and shape the course of history. Many people attempted to access these powers, to different degrees depending on their theology and cosmology (and credulity): alchemists, astrologers, diviners, conjurers, and necromaners, for starters.
This isn't really a response to your question so I'm fully aware that it will likely get deleted but either way I want to give you a friendly head's up that it can be kind of offensive to refer to schizophrenics as "fascinating" in the distant, clinical tone that you used. I know you probably didn't mean it this way, and that you really are just genuinely interested in the history of the illness, but to refer to schizophrenics as fascinating while observing their lives and delusions from a safe distance tends to objectify and dehumanize the real people who suffer from this illness, as though they are little more than an interesting scientific experiment to be observed, explained and prodded at or just an assortment of funny stories to be collected.
Although Foucault's status in the historical field (and probably in this subreddit) remains controversial, there's no disputing that Madness and Civilization remains the most game-changing analysis of the history of mental illness and the ways in which manifestations of mental illness are socially and culturally constructed. Read the portion of the first chapter that deals with the ship of fools, which is probably the most eloquent and thoughtful metaphor you'll ever encounter, and then skip to chapter two, "The Great Confinement."