(Sorry for the English -- Mein Deutsch ist noch nicht so gut.)
I'm in a similar position to you two--social science Doktorand--and the iLiad has been absolutely perfect for me. Big enough for journal / book PDFs, annotation worked great, and the notetaking was great for conferences, usw. Of course, a month ago I fell off my bike and cracked the screen! For me, I think it's worth it to get mine fixed (even at a ridiculous $275 for the repairs) and then perhaps get a Notion Ink Adam or something else next-generation in the fall--but unless you see a cheap, used iLiad, that doesn't help you much.
What I would suggest, though, is to wait for the upcoming firmware release on the Irex DR800. If it indeed enables annotation, and makes it as good as it was on the iLiad, that sounds ideal for your purposes--at least if you can get the cheaper US version.