  The thermoelectric (TE) properties of a material are dramatically altered
when electron-electron interactions become the dominant scattering mechanism.
In the degenerate hydrodynamic regime, the thermal conductivity is reduced and
becomes a {\it decreasing} function of the electronic temperature, due to a
violation of the Wiedemann-Franz (WF) law. We here show how this peculiar
temperature dependence gives rise to new striking TE phenomena. These include
an 80-fold increase in TE efficiency compared to the WF regime, dramatic
qualitative changes in the steady state temperature profile, and an anomalously
large Thomson effect. In graphene, which we pay special attention to here,
these effects are further amplified due to a doubling of the thermopower.
