I always used to think hi viz stuff made folk look silly and I never wore it. That was before I learned to drive. I now realise how easy it is for car drivers to not see cyclists, even in the daytime.
So I often wear hi viz in the day, especially on long runs. I always wear hi viz with reflective strips at night, along with a reflective "snap on" on my ankle and loads of lights.
This evening I was driving down an unlit country road that I often cycle down on my way home from work, and there was a cyclist with no hi viz and little reflective wear with only a flashing red light. I did not really see him properly until I was quite close. Made me realise that my "look as bright as possible" thing is the right approach.
It's all well and good worrying about looking a berk in hi viz, or saying that drivers should pay more attention. But that is all academic if you end up getting killed or badly maimed.
Safety comes first for me - I will leave the fashion and pious pontificating to other reckless fools.