Thanks for all the info so far guys.

To be clear my main expectation for use is to charge my iPhone 6+ on tour. I use it for navigation and photos during the day and communication, weather tracking at night. I download maps ahead of time and turn off the cellular connection during the day to reduce battery drain. I expect this new phone will get close to making it a whole day without a recharge, but might not quite, though this can be easily dealt with by charging at lunch. I'll also be charing a headlamp, and on future trips a camera but these can easily go a couple days, even a week without a fresh charge. Sometimes usage can get heavy in the evening (photo editing, blogging), so I'm guessing my back-up battery will make it two days, 3 if I'm careful. On most trips, recharging every 2-3 days won't be too hard, but it would nice to have the flexibility and not have the anxiety of worrying about if my power will make it to the next charge.

Regarding the second wheel build, I already have a spare rim and I do my own wheel-building so its really the cost of the spokes (nominal) and hub (not so nominal). The rim is a Mavic 217, 28 spoke, not suitable for touring, and I'd rather not run the heavy touring wheels for semi-sporty rides around town and the local countryside.

Does anyone have any recommendations for the newer, better-quality tire-rolling generators? That might be easier for swapping wheels, and I like the idea of being able to turn it off completely with no drag when not in use.. Honestly, the hub might be more useful for my summer around town wheels.