I've been involved in marketing plenty of things, but never books unfortunately. So I'm limited in sharing any experience with you that might help. That said, with the eggroll book in particular, what about shooting some video prep of a few recipes from the book and getting them on you tube. Loads of foodie forums you could get onto and get the word spread through foodie networks and so on. The eggroll book strikes me as being one that lends itself to some pretty easy marketing avenues.
The other two, well I don't see any potential there for video marketing, but specific community forums again would be great places to perhaps introduce yourself and the books to the right kind of people.
At the moment it would seem that your sales are coming from buyers who essentially stumble upon them, rather than come specifically looking for them. So I think your aim needs to be to generate some buzz within groups that have a passion for what the books speak to.
Really unique and exciting products to work with, so good luck with the sales on those!