Suppose an author I like says she'll write a new work if she gets enough donations. Under CDT, it's clear to me that it can't make sense for me to donate - my donation can't increase the probability of me reading the book enough to pay for the cost, and there are much more efficient ways for me to give altruistically. What do other decision theories have to say about this?

Short answer: CDT doesn't donate. EDT, TDT and UDT all donate (assuming enough others are mutually known to be like you).

TDT was literally made for this kind of situation (because it's just a Newcomblike problem). UDT differs from TDT only in areas a bit more obscure than this. EDT is also designed to handle this perfectly too (ie. to get you the book for minimal price). If you donate evidence does suggest that enough people will donate to get you the book but if you don't donate evidence suggests that you will not.