How much easier is it to get agented for a work of fiction once you have a couple of published non-fiction titles to your name?
I won't lie - it certainly helps. Because it shows that you can write enough words to finish a book; because you've been through the publishing process before and will be more understanding of it; because you can, in all probability, write; because you'll already have a readership. However, some agents believe you should just pick one form of writing - either fiction or non-fiction or children's - and stick to it, so not every agent may agree with me on this one. But I'd certainly always read a submission, at least, from this sort of author and I'd usually make it a priority.