There are some instances where two doctorates are plausible. My friend (on whose computer I am typing this) already holds a PhD in experimental psychology (a typical research PhD), but is currently studying for a DClinPsy (clinical psychology doctorate, which is a professional training in psychotherapy) like my girlfriend. However, these are two very different qualifications, and he is learning different things from them.
It is pointless having two research doctorates, but if there is something fundamentally different to the other doctorate, e.g. it is a vocational taught qualification, then it may be worth it. Prestige of the university alone is not worth it.