So right now books are pretty worthless to get, and in fact are almost never worth the trouble they cause. I would like to suggest a change to this to make it more valuable to obtain.
First is the tomes. Rather then awarding xp and money, tomes should reward crafting materials specifically it should reward Diamantine, at 15~25 a piece this would be a great incentive to want to get them
Next are grims, Grims in DT are FAR more challenging to deal with then in VT as the corruption system in DT is much more punishing then in VT. I would suggest, that because of the lack of loot at the end of levels, Grims should reward a guaranteed blue item if you successfully carry 1 grim back, and a purple item if you bring 2 of them back.