I didn't try this mechanism yet, but it seems to be a good idea to get random scrolls using pixie dust. Since pixies are erratic, a random scroll fits here. However the bigger is better.
If you can only make scrolls of known spells, it wouldn't be so much fun to try, since you know what you will get.
Practically it would only be good to give them for the other characters, which don't know that spell.
As an alternative pixie dust could make random spells and there could be something else instead of pixie dust which would allow to 'scrollize' our own spells.
