The 'soap opera effect' is just a learned response. People are used to movies at 24hz and games at 30hz so that seeing either at a higher framerate makes them feel 'off'. It's a response that needs to be unlearned.
It's the same reason that people freaked out over The Hobbit at 48 fps; the higher framerate is enormously useful when it comes to 3D but people associate it with soap operas.
It would look the same but halve the input latency. Most inputs are already doing that though and there are more important links in the display chain. There's a pretty decent article on the subject
here.
Your USB mouse should have a poll rate of 125hz which is 8ms of latency. That's very slight next to a vsynced 60hz game having 17ms and 30hz game having 33ms of latency.