There have been cases when even with expert Wisdom the box turned out to be empty, and I don’t even know what I missed out on
You just need to clearly distinguish what exactly and which box allows. If it contains a specific school — you are allowed to use scrolls of any level from that same school. If it’s a specific level — then scrolls of any school of that level.
The only tricky case is when a hero with basic Wisdom ate an empty box — what was there, level 4 or level 5? In short, we need to think it over...
I understand that it would be too convoluted if we tried to formulate a corresponding clause in the rules, but it’s such a shame when you lack Wisdom, you defeat hordes or packs of powerful monsters, lose a lot of troops, and end up with diddly squat. It’s clear that the very word "Pandora" speaks for itself, but as Dreamcatcher rightly noted, if you have the scroll, you don’t need Wisdom — you just need to build the appropriate Mage Guild.
p.s. I needed to bump the thread, and this opportunity came up =)