This is a GREAT subject. We as humans are really bad at picking what to worry about. We worry about air flight, which is very safe, but not about being in cars (don't we all know someone who has been in a serious car accident?) We worry about stranger abduction when in reality it is very rare.
So, riding... I always wear a helmet, but I roll through stop signs if I can see no one is coming. I've recently taken up a glasses mounted mirror, but really wonder if it will really ever prevent an accident.
I've gone from 193 to 149 pounds and my blood pressure is now normal. I enjoy my bike commute. I enjoy spending time with my wife who has taken up riding.
Risk/reward? Who really knows? Are there even good stats that would be relevant for me? Stats that factor out kids, crazy 20-somethings and the clueless? I haven't seen 'em.
So like everyone else, I go by gut, rationalization, guessing, hope and end up doing what I want.

This doesn't really help you much, does it?