My opinion of it, is it may FEEL safer, but if you are not behaving as pedestrian like as possible, then you are just adding to your risk factor.
IMO about 7mph is reasonable on a sidewalk...just pay attention. The real risk factor is at interesctions and parking lots, where a car may either not notice you or miscalculate your speed.
Most often I'e seen are cars will block the pedestrian lane (sidewalk or crosswalk), often requiring a speeding rider to have no nail the brakes. The other is right hand turns, where they don't notice the rider until they just hit them. It's those two situations alone why I keep insisting if anyone rides the sidewalk, while they are to behave like a pedestrian.
The other side is pedestrian safety....if they don't feel safe with the way a person is riding their bike on the sidewalk...then they either need to adjust their riding style or get on the road....after all, a sidewalk was designed explicitly for pedestrians, while roads were designed for vehicles (like bikes).
basically it boils down to rideaccordng to the path you are on, and what you feel is safe on a sidewalk doesn't matter...it's whats safe to the people walking it that matters.