It's funny you should mention the broadness of the bioinformatics fields. That's something I've been having a problem with. It's been difficult to define what it is I'm exactly interested in, when bioinformatics as a term itself is so enigmatic. Biology, computers, maybe statistics? I wish it were a bit more rigid, just for the benefit of being more of a guidepost ; )
You mentioned you went from bioinformatics to medical informatics. Do you see the two fields as distinct, or as a subset of one another?