Agreed - I think the potential value is quite high in unusual root causes. It's going to be very hard to make a system better at diagnosing 'flu' than a trained clinician. However, "flu-like-symptoms" plus a couple of subtle things in the history may point at a relatively obscure syndrome or whatever, which can be very difficult for a clinician to find.

Another thing to consider in any work like this, you really need to thank about what your false positives mean, in a practical sense. If your numbers are big enough (e.g. screening) and your positives result in a procedure (e.g. biopsy), eventually someone is going to die based on a false positive. This may still be the better option, of course, but you really need to demonstrate that, and think about what your sensitivity and specificity tuning needs.