BentMikey said:
I'm having a hard time imagining decent lights not being visible in the way hiviz can so easily be missed.
At night, no question, lights are king. In twilight and full light, I don't think it is as clear cut. It will depend on lots of factors, traffic volume (the more traffic, the more likely that lights will blend in with the plethora of other lights), the angle of traffic approach to you, the prevailing background colours etc.
In general all visual aids help with visibility, and their effectiveness will vary from situation to situation.
I should add, though, in the summer I won't be using lights, and won't have traditional hi-viz on. I tend to go for contrasting colours, i.e. bright top, dark shorts etc. Solid colour is your biggest enemy IMO.