Sorry john, may have read your post too negatively. To clarify, does the igaro work for you or not? Do you think you could cut free from the mains with it on a long trip like yours.
For the speed which I cycle at this time, the USB for charging is all but useless.
The only time I plug anything into it is when I'm on a flat road with the wind behind and I'm likely to be riding like this for hours, and even then I find I'm only plugging in to it because it's there and I'm in hope that every little helps. If I were to build a bike from scratch with what I have experienced, a dynamo would not exist.
The 400 or 500 sobs for the lights, dynamo, and USB adaptor, would not be a part of the build. I would simply buy good battery front and rear lights, because I rarely even ride in the dark and don't go through enough tunnels. Battery lights would last a very long time with me, and batteries are dirt cheap anyway, especially considering LED lights use hardly anything.
But that's me. I could imagine the dynamo would be a much better investment for roadies who maintain a fast pace for a large part of their ride. Or even those who travel ultralight and fast, but as I don't ride like that, I couldn't tell you if that setup would be worth it for sure.
Take into account also that things break, this would be really upsetting. I had to have my dealer look at the lights because they started to turn on each time I hit a bump, so reaching down to keep turning them off was a pain. They seem OK now, but at one point I unplugged the lights from the dynamo because it was annoying me. If they break altogether its expensive for another set of lights and I would end up with battery lights anyway.
My advice to you: Save your money and buy battery lights.