I love my "Little Red Fire Engine". Dry Fusion earns me loads of cash and does a great job. Even jobs you think wouldn't be possible this side of a good rinse/extraction set up.
There are limits however. The system is designed to clean between 10 and 20 sqM per pad. In a residential environment, after moving furniture to the middle of the room or wherever, it's not unusual to find that you are cleaning an area of, lets say, 3 sqM. This will mean that you are, relatively speaking, overwetting the the carpet so you loose the 30 minute drying advantage, and you product cost can therefore go through the roof. The same applies to other LM systems too.
I know what you mean by getting older and the stamina issues, so have you though about working smarter rather than harder?
Safe and happy cleaning

The Ken