» Thu May 26, 2011 8:10 pm
In general, if you can sell something , you don't need it any more. The developers were (excessively) cautious about making things quests objects so you couldn't lose them by mistake, so if you ARE able to drop, sell or whatever an item, you can really do without it.
IIRC you can actually get further copies of the book, but only once you've done this quest, so if you didn't read it (it's a skill book like all of the series) you get a second chance to bump up Illusion later on.