How much safer does painting prop tips make a plane?
An FAA study looked into that, it's titled: A Review of Civil Aviation Propeller-to-Person Accidents: 1980-1989.

This part stands out:


  While propeller and rotor paint schemes may reduce the number of propeller-to-person accidents, there is little information available regarding the various circumstances surrounding the accidents that do occur.


So there is little information. Their summary is:


  Persons most at risk for a propeller-to-person accident are deplaning passengers and passengers attempting to assist the pilot. That finding clearly assigns considerable responsibility to pilots to ensure safety of their passengers in this regard.


As you see, they did not stress on the paint, they also highlight that since the past, propeller driven aircraft are no longer the most popular type [for civil air transport].

An older study but relevant was conducted by the US Army. The document does not list accidents or statistics, so it's safe to assume it's a precaution. Better safe than sorry.

And in an environment such as an aircraft carrier's deck at night, it most certainly helps (but that's my opinion), there isn't a control set for a scientific assessment (as far as I can tell).