I actually like the idea of a speaker. If you use an earphone you often have to jack the volume up loud which can destroy your hearing. When I do use earbuds, I use noise isolating ones, the kind that act as earplugs, that way I don't have to turn the volume up loud, I can listen at a lower level. I don't use them on the bicycle, so far, but do use them on the motorcycle. On a motorcycle it is advisable to use earplugs to cut the wind noise, even with a helmet. The wind noise is very damaging to your hearing and fatigues you quickly. I ride long distance and my ears would ring after a 700+ mile day. With earplugs I can hear cars, sirens, etc. better since it cuts the wind noise.

For tours on the bicycle I have considered a speaker as well. I wouldn't want to blast the sound but want to hear it. It depends on where I was. If I was on a lonesome stretch of highway, who would care?