Thanks for playing and for the idea. In the end it seems you were 100% right judging from general lack of feedback.
I was thinking about some sort of decoding table for the password system. The only conditions it needs to satisfy is obscuring available passwords and be somewhat simple to use.
I would say that teleporting at will is a no-no in a metroidvania, especially when there are gimmicks like the one at the end part (since all of those are separate pages, that would let you escape). I have ideas for fast travel, but the only way to make usual navigating less cumbersome are shortcuts and condensing the content.
Stuff like lenses are of course an option. For example magnifying glass would be used to search for tiny clues, ultraviolet light that was originally supposed to be used for the dark rooms, and either lenses or cards with holes for decoding texts.
Touch screens already have page turning through swipe. I guess it would be a good idea to port it for mouse controls.