I believe talk of the dantain is more confusing then helpful. It's just another vague word that is hard to pin down. Firstly it's from a foreign culture (for most of us). Secondly it's an old world word.
If we want to define amongst ourselves what it means that's great, but otherwise it's just confusing.
Actually Chris, it's only a "vague" word for those without access to a teacher that doesn't have those skills. For those that have access to a teacher with the skills, and to those that have the skills, it's not vague at all
Certainly Abe Sensei in Kyoto isn't "vague" at all when he talks about the tanden and what to do with it.