String (and other) Theories . . .
Okay, why is Harley Quinn holding a plumb-Bob? And the Pompous Old Fop a string to a cannon, too? Could it be that we are supposed to measure the images with a certain length of bendable string, not a ruler?
In math, there is Euler's Constant, which shows us why a spiral is a spiral of a certain ratio like a hurricane or a nautilus shell. (Did I mention I hate math?) This constant also can go by the name "The Golden Key".
For the less math inclined, there is also the home page of writer George MacDonald, who was a Christian Fantasy writer (passed in 1905) who did a lot with myths and legends and wrote a second book in a series called "Dealings with the Fairies" by the name of "The Golden Key". This might explain the "God!" remark by Harley Quinn, the books behind him, and the appearance of fairies Celeste and Zodiose.
A few things about keys in general that a locksmith would know better:
Keys are based and cut on several different levels, like 1-octave of a musical scale. Thus, the orange keys on the "KEY" page, may actually have letters and play music. Keys also have different size and shaped heads to determine what is a boat, house, car, lawnmower, or vault key. This would also fit with the idea of a musical "key" and "measure".
A key is also a type of beach formation, which may explain why Fandango, in the last page ("LOVE") is looking over his shoulder, suggesting we may do a little surveyor's siting from a particular point that is the second-to-last step away from where the key is hidden. So "To the highest point!" may be right, but only as somewhere to park for a while with a telescope -- thereby not violating any National Park laws.
As for an on/off theory about the Stars:
I thought at one time "To the highest point" might relate to the highest star on each page, and doing something with that single star.
I also though that the Star Riddle came out to POE not POEm -- because of a connection with Edgar Allen Poe's treasure hunt story "The Gold Bug" -- where at a critical moment one of the main characters makes a mistake in an angular distance because he sites with his left eye and not his right. So I tried getting words from going to the pupil of each right-eye to right-eye. (Neptune's beard was a nightmare!) From there I divided the letters I hit into red, white, blue, and stars. White letter bunches could use other colors, but each color then formed a subset for it's own word (like "ISLAND" or "PACE FORTY...")
Great vlog post MCD777!
Bytes, I like your idea. I often think about how Fenn might painstakingly used some constraint to tip off a keen observer.