I became interested in power assist for touring. We had also found ourselves planning tours and side trips around the terrain rather than where we'd like to tour and what we'd like to see. Having power assists allows us to tour many more places and take all the side trips we'd been passing up. The other common option is electric which is a good alternative for around town and commuting. Electric assist tends to be heavier for the power output but reasonable systems can be built.
Gas is readily available on the road and quite inexpensive.
We can also use it in our stove in a pinch. Finding a small low power gasoline motor is a trick though. The smallest available are string trimmer motors of about 20 cc displacement. These develop about 1 HP, or 750 watts. This is more, and thus heavier, than needed but again is about the smallest available.