The OP asks for a single-word or concept which can account for the two different aspects of the situation described.
1) a term for “folks [who] insist [an] idea is so brilliant and visionary precisely because it's incomprehensible”
2) What to call vaguely pretentious-sounding amphigories, spouted in order to trick others into believing it is a valid piece of awe-inspiring genius?
User ermanen, has suggested The Genius Effect, a concept which astutely addresses the first aspect of this OP (see the link in comment below OP).
I offer a term for the second.
• the use of reasoning or arguments that sound correct but are actually false.
• a reason or argument that sounds correct but is actually false.
sophistry sophistry (n.) "specious but fallacious reasoning," mid-14c., from Old French sophistrie (Modern French sophisterie), from Medieval Latin sophistria, from Latin sophista, sophistes (see sophist). "Sophistry applies to reasoning as sophism to a single argument" [Century Dictionary].
sophist (n.) "one who makes use of fallacious arguments," mid-15c., earlier sophister (late 14c.), from Latin sophista, sophistes, from Greek sophistes "a master of one's craft; a wise or prudent man, one clever in matters of daily life," from sophizesthai "to become wise or learned," from sophos "skilled in a handicraft, cunning in one's craft; clever in matters of everyday life, shrewd; skilled in the sciences, learned; clever; too clever," of unknown origin. Greek sophistes came to mean "one who gives intellectual instruction for pay," and at Athens, contrasted with "philosopher," it became a term of contempt.
Sophists taught before the development of logic and grammar, when skill in reasoning and in disputation could not be accurately distinguished, and thus they came to attach great value to quibbles, which soon brought them into contempt. [Century Dictionary]