  Realistic vacuum $\pi\pi$ interactions are employed to investigate thermal
$\pi^+\pi^-$ emission spectra from the late stages of heavy-ion reactions at
ultrarelativistic energies. Hadronic in-medium effects, including many-body
$\rho$-meson spectral functions used earlier to describe the dilepton excess
observed at CERN-SPS energies, are implemented to assess resulting
modifications in relation to recent measurements of $\pi^+\pi^-$ invariant-mass
spectra by the STAR collaboration in $p$-$p$ and $Au$-$Au$ collisions at
$\sqrt{s_{NN}}$=200 GeV. Statistical model estimates for the $\rho^0/\pi^-$ and
$K^*/K$ ratios close to the expected thermal freezeout are also given.
