Your conclusion is a non sequitur. While people cannot discern individual events a 60Hz, most will perceive a CRT monitor as slightly but disconcertingly flickering, an effect that only vanishes at 70Hz or more (I once had a co-worker who didn't notice that 60Hz flicker and opted for more pixels over higher frequency in his XF86Config, nobody else could look at his monitor for extended periods of time...).
So there definitely is some room for quality improvements above 30Hz, but the amount depends on the viewer and the technology (flat screens do not flicker even at 60Hz, and it is almost always preferable if you animation frame rate is the same as you video refresh rate [edit: or an integer fraction thereof. From which premise we can mathematically prove that there is only one acceptable frame rate for TV sets: the least common multiple of 30Hz (NTSC video), 25Hz (PAL and SECAM video) and 24Hz (movies), which happens to be 600Hz. Way to go, my dear marketing departments.] ).
So there definitely is some room for quality improvements above 30Hz, but the amount depends on the viewer and the technology (flat screens do not flicker even at 60Hz, and it is almost always preferable if you animation frame rate is the same as you video refresh rate [edit: or an integer fraction thereof. From which premise we can mathematically prove that there is only one acceptable frame rate for TV sets: the least common multiple of 30Hz (NTSC video), 25Hz (PAL and SECAM video) and 24Hz (movies), which happens to be 600Hz. Way to go, my dear marketing departments.] ).