I was at Hermosa last year in May during one of the first decent south swells, and it was probably 8 ft and closing out, no one out. Getting outside looked doable, but it seemed like it was just death to be able to make a wave.
Although salinity does influence density, there's more of an effect on water density from temperature than salinity. I may have mentioned this before... studies of rocky coastlines with similar geomorphology, swell energy, and rock type have shown greater erosion rates in colder water than warmer water. Scientists believe temperature plays a significant role in the energy of a breaking wave... increased density means more energy from the same sized wave.
Salinity does fluctuate along the shoreline, but it has more to do with tidal fluctuations, runoff and seepage than temperature. Heavy rains lower salinity as that water makes its way into the surf zone and is flushed out with the outgoing tide.