This post answered a *ton* of questions for me as well, regarding who could use cards when and how -- just helped me connections in a bunch of fuzzy areas. In absence of more specifics in the game instructions, we were falling back on RPG assumptions like most others here. Blargh.
A paragraph in the "Attempting a Check" section covering "Determining Whether To Acquire a Boon" might cover it. Something like:
"All characters may acquire any boon they encounter. All characters can use that boon at least once, depending on their character's traits. Use instructions on the boon and on the character's card to determine how the boon may be used with that specific character."
Like Ogee, we were banishing all the spells that came up, because we read the card as something you couldn't acquire if you didn't have the arcane trait. A paragraph like the one above might have cleared that up for us.
We are really loving the game -- even got my mom playing it, who says "I've never seen dice like these before!" She's been visiting for a week, and we've played almost every day. :)