If the problem was "people are driving too fast" then telling them to drive slower is a reasonable solution. But that is not the problem.

The problem is that people drive in a manner that is less attentive than they should for the situation. Speed is but a symptom of this. Fear of financial punishment should be combined with other methods to encourage safer driving.

Changing the speed limit without making other changes to a road (speed humps, raised intersections, obstacles preventing straight travel, etc) won't change the speed at which drivers are comfortable going. Sure, it will encourage drivers to make the intellectual decision to slow down ("I'll drive slower to avoid a ticket."), but thanks to a myriad of reasons (not paying attention, distracting children, ignorance, etc) we also need to make changes that cause drivers to intuitively drive slower.

I am for the lowering of speed limits, don't get me wrong, but it shouldn't be expected to make as big of a difference as we'd like for safe residential streets where people of all ages can truly thrive.