I doubt it; it's the signal/noise ratio that matters, not the absolute difference, and multipath reflections (that aren't compensated for) look just like noise.
As far as transmission power goes, basically, you need enough to reach the horizon with an acceptable S/N ratio, but that's already true of most full-power UHF stations.
Low-power UHF and full-power VHF stations are another matter; I'd like to see the FCC cut both of those a bit more slack, as long as interference guidelines are still met. (Not long ago, the FCC gave low-power VHF stations a big break, raising their max. ERP limit from 300 watts to 3000, and I think it did help the few low-power VHF stations we have.)